1. Introduction
Sustainable Development Goal 4 (SDG 4) emphasizes the transformation of education systems to promote the competencies that help citizens face our current challenges in the context of climate change and ecological crisis. Professional development provides continual learning and conscious reflection to respond effectively to change in professional practice, which implies that professional development can enhance quality education and help meet SDGs. It can be supported through informal or formal activities, such as accreditation schemes, in-service training, workshops, coaching, workplace projects, and professional learning community.
However, it has been reported that professional development is more effective when it is connected to the particular context of the institution or program, involves collaboration and cooperation among teachers, and is related to program objectives and student learning [
1]. Based on findings [
2,
3,
4,
5], cooperative professional development (CPD) has been acknowledged as essential for facilitating teachers’ competencies. CPD includes various activities such as peer observations, team teaching, research activities among colleagues, and a professional learning community (PLC), which are even considered for teachers to be a factor for successfully implementing the revised curriculum [
6].
School principals’ leadership style was paid special attention as an effective lever of CPD [
7,
8,
9,
10,
11,
12,
13]. It has been reported that transformational leadership is more efficient than transactional leadership that does not strive for cultural change, favors top-down management, and is often silent on the manager’s decision-making [
14]. Similarly, it can be applied in the context of ESD [
15,
16,
17]. Transformational principals can function as critical agents for creating the school vision in the framework of ESD, promoting practices that will facilitate ESD, and assisting teachers in developing deep competencies for ESD.
These can be activated better when principals discuss the necessity and significance of ESD together with teachers and allow teachers to be involved in decision-making. Pittman also [
18] proposed participatory management structures as an integral element for sustainable development in an educational context, which implies transformational leadership that invites teachers to share decision-making authority. Korean schools have crafted and carried out their operation plan every year based on the National Curriculum and a particular school context. ESD was well-positioned as one of the cross-curricular themes in the 2015 revised National Curriculum [
19]; however, the degree to which cross-curricular themes should be dealt with varies significantly, depending on circumstances facing schools and teachers’ readiness or will. Therefore, transformative leadership is more highlighted to facilitate ESD in Korea.
Focusing on the promising role of principals’ leadership, some researchers have revealed the effect of transformative leadership on CPD [
7,
20,
21,
22,
23,
24,
25], along with the researchers’ efforts to elucidate the effect of transformation leadership on teachers’ self-efficacy [
26,
27,
28,
29] and teachers’ attitudes [
30]. It has been shown that teachers’ self-efficacy and attitudes are major predictors of CPD [
23,
24,
25]. Furthermore, it has been reported that teachers’ self-efficacy mediates the relationship between transformative leadership and CPD [
31,
32,
33], while a few studies have illustrated the effects of self-efficacy on attitudes [
34,
35,
36,
37].
Taken together with empirical evidence, there can be a gap in understanding the relationships of transformative leadership, teachers’ self-efficacy, and CPD in a model. As an alternative, the model may include two mediators, self-efficacy and attitudes, in the relationship between transformational leadership and CPD. The inclusion of justifiable variables in the relationship between transformative leadership and CPD helps to elucidate the linkage between transformative leadership and CPD in ESD. Based on this relationship, the hypothetical model of principals’ transformational leadership, teachers’ self-efficacy in ESD, teachers’ attitude toward ESD, and CPD can also be established. Exploring the underlying mechanisms through which transformational leadership stimulates CPD is the first step to precisely explain how transformational leaders produce positive outcomes such as CPD.
Moreover, these variables, such as teachers’ self-efficacy and attitudes, are deemed to have a pivotal role for CPD, suggesting a greater understanding of the relationship between transformational leadership and self-efficacy, attitudes, and CPD. Therefore, there is a need to examine empirically in the hypothetical model with two mediators of teachers’ self-efficacy in ESD, attitudes toward ESD, to explain better the relationships between transformational leadership and CPD in the context of ESD.
Nevertheless, while looking at the link between transformative leadership and CPD, there is still a dearth of studies on the mechanisms explaining how transformational leadership positively affects CPD, focusing on this possible mechanism (transformative leadership—self-efficacy—attitudes—CPD). Furthermore, the hypothetical mechanism has also not gained much attention in the context of ESD; however, it still has to be highlighted. Therefore, the author considered the serial multiple mediation model to predict teachers’ CPD in the context of ESD.
Thus, the author aimed to test a serial multiple mediation model with two mediators to explain the mechanism that underlies the relationship between principals’ transformative leadership and CPD in the context of ESD, and to estimate and test specific mediation effects. Based on this purpose, the following research questions were addressed in this research.
RQ1: Does transformational leadership positively influence CPD related to ESD directly or indirectly?
RQ2: Does teachers’ self-efficacy in ESD mediate the relationship between transformational leadership and CPD?
RQ3: Do teachers’ attitudes toward ESD mediate the relationship between transformational leadership and CPD?
RQ4: Do teachers’ self-efficacy in ESD and their attitudes toward ESD mediate the relationship between transformational leadership and CPD in serial?
Unlike prior studies, which either investigated the effect of the variables mentioned above on each other separately [
38] or focused on their relationships without considering ESD [
8,
9,
10,
11,
12,
13], this study tested the relationships of transformative leadership, teachers’ self-efficacy, and CPD in a model. This approach is first in the context of ESD, to my knowledge, which will be able to make a significant contribution to the existing literature on transformational leadership, teachers’ self-efficacy in ESD, teachers’ attitudes toward ESD, and CPD.
2. Literature Review
2.1. Transformational Leadership and ESD
Principals are gaining attention as vital factors in the framework of ESD because they are in a position to shape the organizational conditions necessary for successful and sustained implementation, create the school vision, and set high expectations and explicit purposes [
39,
40,
41]. Thus, researchers bring forward the roles of a principal as a transformational leader because transformational leadership can be considered a vital agent for building the school’s organizational capacity and creating the cultural and structural conditions for meaningful and effective teaching and learning [
42,
43].
Transformational leadership is defined as a leadership approach that causes a change in individuals and social systems. Burns theorized that transformational and transactional leadership were mutually exclusive styles. Transactional leadership usually does not strive for organizational cultural change, while transformational leadership tries to change the organizational culture [
14]. Recently, with growing interest in sharing decision-making authority, it has been approached as a dimension of transformational leadership. Pittman [
18] proposes elements that are integral to success for sustainable development in an educational context. These include institutional commitment, shared vision of the future, participatory management structures, and external partnerships, which emphasize the need for shared decision-making authority and are related to transformational leadership [
44].
With growing interest in the significance of transformational leadership in the educational setting, researchers have analyzed relations among transformational leadership, teachers’ efficacy, teachers’ attitudes, and teachers’ participation in CPD. The relationships among variables were discussed more specifically in the following section, based on the related literature and empirical evidence.
2.2. Relationship between Transformational Leadership and Teachers’ CPD
As a step toward constructing a conceptual framework for the study, the researcher reviewed the extensive research on teachers’ participation in cooperative professional development (CPD). CPD is defined as any activity in which two or more teachers work together for their professional growth, and Glatthorn [
45] used cooperative professional development (CPD) as an inclusive term to embrace forms of peer-oriented systems. Recently, transformational leadership has been acknowledged as an essential factor in facilitating CPD [
16,
17,
18]. Furthermore, the findings have shown a relationship between a leader’s transformational leadership and CPD [
8,
9,
10,
11,
12,
20,
21,
22,
23,
24,
25]. Therefore, considering this evidence, it is likely that transformational leadership will impact teachers’ CPD in the context of ESD either directly or indirectly. Thus, the following hypothesis (H1) was established.
Hypothesis 1 (H1). Transformational leadership will have a positive effect on teachers’ CPD directly or indirectly.
Hypothesis one requires testing of both direct and indirect effects. Thus, two sub-hypotheses were established: a hypothesis on the direct effect (H1a) and the indirect effect (H1b). Hypothesis one can be considered to be rejected when both hypotheses are not accepted.
Hypothesis 1a (H1a): Transformational leadership will have a positive effect on teachers’ CPD directly.
Hypothesis 1b (H1b): Transformational leadership will have a positive effect on teachers’ CPD indirectly.
2.3. Relationship among Transformative Leadership, Teachers’ Efficacy, and CPD
Transformational principals can foster individual accountability in implementing ESD, provide teachers with vicarious experiences by demonstrating good models for implementing ESD, and facilitate teachers to master knowledge and skills in ESD. As a result, teachers’ efficacy can be strengthened. Research findings have reported empirical evidence that transformational leadership has significantly positive effects on teachers’ self-efficacy [
26,
27,
28,
29,
34,
35,
36,
37].
Guthrie and Schwoerer [
46] proposed that individuals with higher self-efficacy levels are most likely to have positive attitudes toward learning, a belief that there are benefits to be gained from participation in such activities, and a greater awareness of their specific development needs. Prior research has reported that teachers with high self-efficacy are more likely to participate in professional development than those with lower self-efficacy [
47]. Similarly, Lohman [
48] also reported that teachers’ self-efficacy is one of the most critical factors affecting teachers’ participation in learning activities. In a study of the factors that influence teachers’ participation in CPD, their self-efficacy has a significant effect on teachers’ CPD [
23,
24,
25].
Taking together the evidence, transformational leadership will affect teachers’ self-efficacy in ESD, and teachers’ self-efficacy will influence teachers’ CPD. Also, considering H1, it is highly likely that self-efficacy will mediate the relationship between transformative leadership and teachers’ CPD. Therefore, the author established the following hypotheses based on the relationship among transformative leadership, teachers’ self-efficacy, and CPD.
Hypothesis 2 (H2). Transformational leadership will affect teachers’ self-efficacy in ESD.
Hypothesis 3 (H3). Teachers’ self-efficacy will affect teachers’ CPD in ESD.
Hypothesis 4 (H4). Teachers’ self-efficacy in ESD will mediate the relationship between transformational leadership and CPD.
2.4. Relationship among Transformative Leadership, Attitude, and CPD
Many researchers emphasize the importance of attitudes toward ESD [
49,
50,
51,
52]. Developing a positive attitude towards sustainability might promote engagement with ESD [
53]. Furthermore, teachers’ perceptions of ESD’s importance play a significant role in their attitudes towards ESD and their willingness to learn about the subject [
52]. Empirical evidence has shown that transformational leadership significantly affects teachers’ attitudes [
54,
55,
56]. Heystek and Terhoven [
57] explain that teachers’ participation in CPD can be motivated by needs such as increased teacher awareness, updating of teacher knowledge, and adoption of new teaching practices. According to Amos and Benton [
58], teachers’ attitudes affect CPD.
Empirical evidence suggests that it is likely that transformational leadership will affect teachers’ attitudes toward ESD, and positive attitudes toward ESD affect participation in CPD related to ESD. Furthermore, teachers’ attitudes will probably also mediate the relationship between transformative leadership and CPD. Therefore, the following hypotheses were established based on the relationship among transformative leadership, teachers’ attitudes, and CPD.
Hypothesis 5 (H5). Transformational leadership will affect teachers’ attitudes toward ESD.
Hypothesis 6 (H6). Teachers’ attitudes toward ESD will influence CPD.
Hypothesis 7 (H7). Teachers’ attitudes toward ESD will mediate the relationship between transformational leadership and CPD.
2.5. Transformative Leadership, Teachers’ Self-Efficacy, Attitude, and CPD
The findings have revealed a positive relationship between teachers’ self-efficacy and positive attitudes towards inclusion [
57,
59,
60,
61,
62,
63]. For example, Wiesel and Dror [
60] stated that Israeli primary school teachers with higher self-efficacy levels had a more positive attitude towards inclusion applications. Lee and Krapfl [
64] also corroborated the significance of self-efficacy in science teaching, identifying a link between teachers’ self-efficacy in teaching science and their attitudes toward science. Similarly, teachers’ positive attitudes are related to firm self-efficacy beliefs in the ESD field also. Gan and Gal [
38] found that a pre-service teacher with high self-efficacy for promoting ESD exhibited positive attitudes towards the environment and pro-environmental behaviors in the private and public spheres. Thus, teachers’ self-efficacy based on teachers’ mastery can influence teachers’ attitudes. It implies that when the teachers believe in their competency to perform their tasks successfully, they likely perceive ESD to be more valuable than the teachers with low self-efficacy, which in turn, may affect CPD related to ESD.
Considering theoretical evidence and above hypotheses (H1, H2, H3) conjointly, it is highly probable that transformational leadership influences teachers’ self-efficacy (M1), which, in turn, affects teachers’ attitudes (M2), resulting in teachers’ CPD. In this process, teachers’ self-efficacy is likely to mediate the relationship between transformational leadership and attitudes. Teachers’ attitudes may also mediate the relationship between teachers’ self-efficacy and CPD. Therefore, the following hypotheses were established.
Hypothesis 8 (H8). Teachers’ self-efficacy in ESD will affect teachers’ attitudes toward ESD.
Hypothesis 9 (H9). Teachers’ self-efficacy in ESD will mediate the relationship between transformational leadership and teachers’ attitudes toward ESD.
Hypothesis 10 (H10). Teachers’ attitudes toward ESD will mediate the relationship between teachers’ self-efficacy in ESD and CPD.
Hypothesis 11 (H11). Teachers’ self-efficacy in ESD and teachers’ attitudes toward ESD will mediate the relationship between transformational leadership and CPD in serial.
5. Conclusions
The process of how transformational leadership exerts its influence has become a growing source of interest. However, there is still a lack of research on the mechanisms explaining how transformational leadership positively exerts CPD in research on the effect of transformational leadership on CPD. Hence, this study aimed to provide empirical evidence that may help in explaining the mechanism through which transformative leadership affects CPD. To this end, the author proposed a serial multiple mediation model that incorporates self-efficacy and attitudes as an underlying mechanism that explains the positive impact transformational leaders have on CPD related to ESD. In addition, the author analyzed specific indirect effects in the relationship of principals’ transformational leadership on CPD using the phantom model approach modeling the specific indirect effects in the hypothetical model. The findings strongly supported predictive links among transformational leadership, self-efficacy in ESD teachers’ attitudes toward ESD, and CPD. Therefore, these findings provide greater insight into transformational leadership and ESD research and reveal mechanisms through which transformational leadership works in ESD contexts.
5.1. Discussion
This study can be discussed in terms of the result findings. First, the effects of transformative leadership on CPD were also confirmed in ESD contexts. This finding supported several prior studies [
7,
8,
9,
10,
11], asserting the significant role of transformational leadership in teachers’ CPD. Therefore, these findings confirmed that transformational leadership is appropriate for making teachers more engaged in CPD, which implies that principals can make a difference in teachers’ CPD.
Second, teachers’ self-efficacy and attitudes, relatively stable traits, were confirmed to predict CPD related to ESD. Also, it is confirmed that transformational leadership can change teachers’ self-efficacy and attitudes towards a positive direction. Therefore, transformational leadership could be a powerful strategy to boost teachers’ self-efficacy and thus to form positive teachers’ attitudes toward ESD. Also, this result supports prior research exploring the effect of self-efficacy on CPD [
26,
27,
28,
29], and is in line with the results of previous studies showing the effect of attitudes on CPD [
58].
Third, the findings demonstrated that teachers’ self-efficacy is a significant predictor of attitude toward ESD. The findings are consistent with Gan and Gal’s [
60] result findings. Revealing the relationship between teachers’ self-efficacy and their attitudes toward ESD will help researchers and teachers make inferences regarding future studies that may help develop positive attitudes towards ESD. Furthermore, this result highlights that sources of self-efficacy in ESD are used as a strategy to develop teachers’ positive attitudes toward ESD because self-efficacy is one of the key determinants of teachers’ attitudes toward ESD.
Furthermore, as assumed in the research model, findings showed that the influence of transformational leadership on CPD depends on the interplay of high self-efficacy in ESD and positive teachers’ attitudes toward ESD. These findings strongly supported predictive links among transformational leadership, self-efficacy in ESD teachers’ attitudes toward ESD, and CPD. To date, no research has investigated the relationship between transformational leadership, teachers’ self-efficacy, teachers’ attitudes toward ESD, and CPD related to ESD, to my knowledge. However, these findings can contribute to some progress in this field because this study investigated transformational leadership, self-efficacy in ESD, and teachers’ attitudes toward ESD simultaneously as predictors of CPD in the context of ESD, applying a structural equation model.
5.2. Implications
This study presents several key findings and has some practical implications for principals, policy-makers, teachers, and researchers regarding teachers’ CPD, practically and theoretically. Above all, as this research showed the indirect effects of transformational leadership on CPD through self-efficacy in ESD and teachers’ attitudes toward ESD, the principals must be aware of all possible causal-chain relationships between transformational leadership and CPD. This causal relation is a challenge for school principals. However, considering CPD’s role in achieving SDGs, the principal must allow teachers to participate in decision-making, promote instructional support, and provide intellectual stimulation. Thus, the author suggests that educational institutions provide proper professional development programs for principal to increase transformational leadership, and principals also have to do their best to improve their transformational leadership.
In addition to practical implications, this study resulted in some progress in ESD field research. These findings help clarify the nature of the relationship between the principals’ transformational leadership and CPD and facilitate a better understanding of the relationship between the principals’ transformational leadership and CPD. Regarding research methodology, specific mediating effects were analyzed using the phantom analysis method, which is still somewhat unfamiliar and innovative in ESD field research. The analysis process of this study may be helpful when researchers try to analyze specific mediating effects using AMOS
Unlike prior studies, which either investigated the effect of the variables mentioned above on each other separately [
38] or focused on their relationships without considering ESD [
8,
9,
10,
11,
12,
13], this study tested the research hypotheses and conceptual model. As a result, this research made a significant contribution to the existing literature on transformational leadership, self-efficacy in ESD, teachers’ attitudes toward ESD, and CPD.
5.3. Limitations and Recommendations for Future Research
This study makes some noteworthy contributions to the existing literature, clarifying the mechanism underlying the relationship between principal transformational leadership practices, teachers’ ESD efficacy and teachers’ attitude toward ESD, and CPD through the Phantom model approach, a novel approach in the field of ESD. However, limitations must be considered. First of all, non-probability convenience sampling was chosen as the sampling method in this study. Therefore, the results of this study might not be generalized to the whole of Korean secondary in-service teachers. Furthermore, in addition to the limitations of sampling, specific themes need to be explored further.
Second, this study did not analyze the relationship between the sub-dimensions of principals’ transformational leadership and teachers’ CPD. To better identify the more precise mechanism underlying the relationship between principals’ transformational leadership and CPD, future study needs to expand the understanding of relationships between sub-dimensions of transformational leadership and teachers’ CPD.
Third, in the context of planned behavior theory (TPA), any behavior is conceptualized in action and target [
82]. For example, regarding teachers’ CPD in ESD topic, teachers’ CPD is a specific behavior, whereas ESD is a target. The author analyzed whether the teachers’ attitudes toward ESD (target), not the attitudes toward CPD, mediate the relationship between the principal’s transformational leadership and the teachers’ CPD to clarify for teachers to participate in CPD related to ESD topic. In future research, teachers’ attitudes toward CPD need to be included and tested to elucidate linkage in the relationship between the principal’s transformational leadership and teachers’ CPD. Although this study has a few limitations, the author hopes to provide a baseline for future research.