Many industrialized countries face an alarming decline in pupils' academic performances as reported by cross-national studies, such as PISA, PIRLS, and TIMSS. For instance, in the Netherlands—where this study was conducted—the trends of the PISA study from 2003 through 2018 show that the average levels of reading and math performance decreased by at least the equivalent of half a year of schooling (OECD, 2019). 

Educational policymakers and schools in many countries are looking for ways to reverse this declining trend and improve achievement levels for all pupils. While the literature on school effectiveness and school improvement provides an impressive account of the factors that may contribute to students' academic achievement (see Hopkins & Reynolds, 2001; Muijs & Reynolds, 2003, 2017), validated evidence of the impact of specific school improvement programmes generally yields very mixed results (Coe, 2009). School improvement studies that focus on specific leadership development programs are rather scarce (see Greany & Earley, 2021).

In this study, we examined the effectiveness of the High Performing Schools (HPS) program, which focuses on improving school leadership and setting up professional learning communities (PLCs) informed by the educational, psychological, and sociological scientific literature. 

The HPS improvement programme was developed by scholars and educators at the Academica University of Applied Sciences in the Netherlands, drawing upon the principles of high-performing organization theory, as informed by the studies of De Waal (2006), Senge (2006), and Hill et al. (2016). The programme has three key elements: whole-school CP{D, focussed on the development of knowledge and skills in teaching and learning, leadership development, based on the Zenger-Folkman model (Zener & Folkman, 2014), and the development of professional learning communities. The theory of change proposes that through the development of high quality professional learning at the school level (using professional learning communities and CPD for both teachers and leaders), we can improve teaching quality, which in turn will improve learning outcomes. In this way we combine insights from research on school improvement, teacher and school effectiveness and professional development. 

The study is confirms within a Dutch context that internationally recognized factors can contribute to effective school improvement programmes here as well, although as mentioned above the primary focus on CPD in HPS makes it relatively straightforward to implement compared to some other approaches which require greater structural change. 

However, what is noteworthy from the international evidence base is that while the core elements of effective school improvement are known, it is nonetheless common for school improvement initiatives to fail (Coe, 2009; Benoliel & Berkovich, 2020; Bryk, 2010). This study can help shed some light on this important question. The findings suggest that, firstly, there is a need to fully integrate all elements of effective school improvement, including teacher collaboration, and, secondly, support the importance of teacher participation and collaboration to make school improvement work. This suggestion, which joins a growing body of research on implementation of school improvement, implies that school improvement requires sustained and intensive focus to succeed (Kyriakides et al., 2021; Supovitz et al., 2019). 

In this study we used a quasi-experimental design in which we evaluated the effectiveness of the HPS intervention by comparison with other schools in the population. The primary sample for this study comprises 47 primary schools that participated in the HPS programme between 2018 and 2021, which we compared with the population of other primary schools in the Netherlands (N = 6,110). For this purpose, we utilized publicly available data on the academic achievement of pupils in Dutch primary schools provided by the Department for the Implementation of Education at two time points. Specifically, we used national data on the results of the high-stakes final test (Eindtoets Basisonderwijs) that all pupils in the country must take at the end of primary school (grade 8), covering reading, writing and mathematics. We examined schools' academic achievement levels at T1 for the school year 2021-2022 while controlling for the achievement levels at T0 at school year 2017-2018. Since participation in the HPS programme is voluntary, there is no random assignment between the intervention and control conditions. As such, it is crucial to ensure that there are no apparent selection effects that can bias the analyses. Therefore, before exploring the effects of the HPS programme, we examine whether there are differences at baseline between schools that participated in the HPS programme and the comparison group. The main analyses were conducted using ANCOVA models.

Overall, the analysis of public data on school achievement suggests that the HPS programme has had a positive impact on overall achievement in the 47 participating schools. Schools that participated in the HPS programme demonstrated greater progress on average than the comparison schools. Furthermore, while a decrease in achievement is evident in the comparison group of schools during the Covid-19 pandemic period, the achievement of schools that participated in the HPS programme did not decline; instead, it improved during the COVID-19 pandemic period. However, the size of the effects varied among the subject areas (math, reading, and writing) and among the two types of HPS programme. We found significant effects for math and writing, while no significant effect was found for reading. There are two explanations for these differences. Comparing different implementation models we found that full implementation of all elements was necessary for positive effects to occur.

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