The last 50 years have seen the birth and evolution of the discipline of educational effectiveness research at an international level. The main aim of this discipline is the estimation of the magnitude of school effects and the study of school, classroom and context factors that characterise an effective school, regardless of the methodological approach taken by the researchers (Murillo, 2005). Ince its inception in the late 1960s, with the publication of the Coleman report (Coleman, 1966), the discipline has evolved from case and outlier studies (Edmonds, 1979; Weber, 1971) to the incorporation of sophisticated methods such as multilevel analysis (Aitkin & Longford, 1986; Goldstein, 1987; Raudenbush & Bryk, 1986) and the generation of integrated models aimed at explaining the relationship between different kinds of student and school factors and student outcome variables (Kyriakides & Creemers, 2008; Scheerens, 1990).

There are several approaches within the study of educational effectiveness, each of which is focused on a different topic. Equal opportunities research deals mainly with the role of socioeconomic and demographic factors in student performance, productive functions research focuses on the effect of school resources on performance, the assessment of compensatory programmes studies their effectiveness at levelling the playing field for disadvantaged students, school effectiveness research focuses on school process characteristics that enhance its effectiveness and, lastly, effective instruction researchers aim to find teachers characteristics that promote a better performance in students (Scheerens & Bosker, 1997).

The present study falls under the school effectiveness category, since it intends to uncover which school-level process factors can make a school more (or less) effective. An effective school is defined as a school that achieves an integral development of all its students, higher than it would be expected according to their previous performance and their social, economic and cultural background (Murillo, 2005). The most common factors associated to school effectiveness in the literature are teacher training, attention to diversity, distributed leadership and teacher participation in school decisions, positive climate, heterogeneous grouping of students or high expectations towards all students, among others (Joaristi, Lizasoain & Azpillaga, 2014; Lizasoain et al., 2015; Murillo, 2007).

In order to select interesting schools to his study builds on a previous research (Gamazo, Martínez-Abad, Olmos-Migueláñez & Rodríguez-Conde, 2018) conducted within the framework of equal opportunities, which studied the main context factors (socioeconomic status, migrant status, gender, school ownership, grade repetition, etc.) related to student performance in PISA 2015 and used this information to estimate the level of effectiveness of schools (difference between a schools actual PISA score and the expected score according to its context) and select schools that scored far above or below their expected performance, thus obtaining highly effective and ineffective schools.

Once the selection was made, there was an attempt to study the school process factors provided by the PISA questionnaires (leadership, teacher participation, autonomy, etc.) with the level of school effectiveness calculated in the previous stage. However, the results were not significant for any of the school level variables (Gamazo et al., 2018). Thus, the qualitative work presented in this paper was undertaken aiming to explore which school-level processes can foster (or hinder) effectiveness.

This study follows a case study design, specifically a collective case study, since it uses more than one case to illustrate the research problem (Creswell, 2007). The sample for this study were two secondary education school selected in a previous study (Gamazo et al., 2018) due to their levels of effectiveness. One school (A) had unusually high levels of effectiveness – their actual score in PISA was much greater than their expected score – and the other (B) presented a high level of ineffectiveness – their actual PISA score was lower than the one expected on the basis of their socioeconomic background. Both schools were located in one of the provincial capitals of the Autonomous Community of Castilla y León, in Spain. The informants interviewed were both teachers and leadership team members (principals, heads of studies, secretaries, etc.) There were three groups of informants in each school: teachers with less than 10 years of experience in the school (novice teachers), teachers with more than 10 years of experience in the school (veteran teachers), and leadership teams. The decision to make these groups was motivated by the aim to gather different perspectives of the school processes. The information was gathered though the organisation of focus groups (6 in total) with 4 to 6 participants each. A previous set of categories was established, based on the research by Lizasoain et al. (2015). This set was composed of nine categories: projects and teacher training, teaching methodologies, attention to diversity and student monitoring, assessment, time management, leadership, school management and organisation, school climate, and families and community. Once the focus groups were conducted and transcribed, the researchers carried out a content analysis consisting of different phases: separation of the information in meaningful units, identification and classification of units, and grouping said units in categories and interpreting them in order to obtain the results. This analysis was carried out with the software NVivo v.XX.

Due to the small sample, both schools presented characteristics associated with high and low effectiveness. However, there were quite a few findings that fall in line with previous research. School A (high effectiveness) presented several traits of highly effective schools, such as: • Implication in training and innovation: both teachers and leaders exhibited a strong commitment with lifelong learning and a notable interest in designing and implementing educational innovations. • Shared leadership: leadership roles are clearly outlined and shared among a large group of people, with decision-making being based on consensus. • School climate: there is a strong focus on the promotion of school climate, evidenced by the existence on many school-side programmes on the matter. • Staff stability. • School assessment: all activities and programmes are assessed to detect improvement areas. • Outside collaboration: the school has established plenty of links with the community in order to organise different educational activities, both in and out of the school grounds. On the other hand, this school presented some traits usually linked with low effectiveness, such as a lack of teamwork among teachers or expectations of student performance linked to student motivation. Although school B presents some high effectiveness characteristics, such as a strong focus on attention to diversity, with two teachers in almost every classroom, and high expectations for all students (it bears mentioning that the school has a high percentage of students with special education needs), it also exhibits many characteristics aligned with low effectiveness, such as: • Negative attitudes towards teacher training. • Low level of systematisation of school coexistence and assessment. • High staff instability. • Low level of teacher participation in decision-making, centralisation of leadership. • Few outside collaborations.

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