Since the publication of the report "Equality of Educational Opportunity" (Coleman et al., 1966), there has been significant progress in the research on school efficacy. Examples of this progress include the following: First, the approach of comprehensive models that bring together the empirical results about the elements affecting academic achievement, which have mainly been used from the 1990s onwards (Murillo, 2016). Second, the use of multilevel analysis techniques that respect the nested structure of the data and, therefore, allow overcoming the limitations associated with the methodological procedures that have traditionally been applied (Blanco-Blanco et al., 2014). Also, the availability of databases from large-scale national and international assessments that, together with measures of students' academic performance, provide information on other personal, family, school, and contextual factors. Finally, the proposal of value-added models that allow to isolate the contribution of schools to students' academic performance after controlling for the effect of external variables.

The research on school effectiveness conducted in recent years has been focusing on factors related to schools and on those located at the classroom level, especially considering teachers’ influence on student learning (Wayne and Youngs, 2003). In this regard, significant progress in identifying the effects of schools on student achievement has been made, with teacher characteristics and competencies emerging among the main determinants of student academic achievement (Hanushek and Woessmann, 2017; Muijs and Reynolds, 2017). In consequence, teacher evaluation has been positioned as one of the key areas of educational research (Escudero, 2019).

Among the teacher variables that have demonstrated the greatest influence on students´ academic outcomes are working conditions –such as years of teaching experience (Harris and Sass, 2011), previous and ongoing teacher training (Glewwe et al., 2011) and salary (Cabrera and Webbink, 2018)– , professional competencies –like knowledge of the discipline (Campbell et al., 2014), classroom management and organization (Ahmad, et al., 2017) or communication skills (Aloe and Becker, 2009), among others.

Therefore, in this contribution we present the results of a meta-analysis based on the studies that have analysed the effect of teacher characteristics and competencies on the academic performance of secondary education students during the last twenty years. The decision of focusing this work on secondary education is due to the fact that the meta-analytical evidence does not show agreement in the results obtained for this educational stage. Furthermore, meta-analyses generally use educational level as a moderating variable, so it is not possible to further investigate the effect of this stage.

Thus, the ultimate purpose of this study is to allow greater knowledge on teacher skills and characteristics that influence student performance from which to base educational policies that generate optimal conditions for a quality teaching-learning process, as well as to contribute to an improvement in the development of the teaching profession.

This study seeks to answer the following questions: What teacher characteristics and competencies have demonstrated the greatest effect on the academic performance of secondary school students? What is the strength of the relationship between teacher characteristics and skills and academic performance?

The systematic review process was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. This process consisted of the following phases: 1. Search for primary studies in the main international databases: Web of Science, Scopus, ERIC and PsycINFO. The search was carried out by means of a three-level structured equation. At the first level, terms related to teacher competencies were included, at the second level, to academic performance, and at the third level, to the educational stage. The search established as a time limit that the articles had been published between January 2000 and December 2019. The equation and search criteria described allowed the retrieval of a total of 2042 records. 2. Initial selection of 104 articles was based on the reading of the title and abstract and on the following criteria: a) type of study: empirical studies aimed at analysing the effect of teacher characteristics and competencies on academic performance, b) type of design: quantitative or mixed, and c) educational stage: secondary education. The papers were reviewed by two researchers, with an inter-rater agreement rate of over 90%. 3. Final selection of articles was based on reading the full text. This phase resulted in the selection of the 44 records with 209 effect sizes that serve as the basis for the present study. 4. Coding of the articles according to the following: a) characteristic or competency analysed (independent variable), b) academic achievement (dependent variable), c) statistic (beta, correlation, ANOVA or Student's t), d) statistics provided to calculate the effect size (size of correlation, standardized regression coefficient, or means, standard deviations and size of the two subgroups) e) number of students, f) number of teachers, g) number of schools, h) educational stage (secondary education or secondary education and more stages), i) country in which the study was conducted, and j) impact factor of the journal in which the study was published. 5. Estimation of the mean effect size. Individual effect sizes were estimated through Fisher's method. A random-effects model was used for the estimation of the summary effect sizes, while a mixed-effects model was used to analyse the differences in the effect sizes according to moderator variables. All of them were estimated using Comprehensive Meta-Analysis (CMA 3.0). The absence of publication bias was demonstrated using funnel plots, the rank correlation test, and the impact factor of the journals.

According to Cohen’s criteria (1992), the average effect size can be classified as medium. This effect size –which is significant at a 99% confidence level– reflects that teacher characteristics and skills explain 10.2 % of the differences in student academic performance. Focusing on the personal characteristics and competencies under consideration, reflective attitudes and teacher professional development have shown the largest effect sizes on student achievement. Regarding pedagogical competencies, the ability to plan and implement the teaching process has demonstrated the greatest effect on the students' academic performance, followed by evaluation skills. On the contrary, classroom management and organisation competency has the smallest effect size on student academic performance. The results obtained report a high level of heterogeneity of the effect sizes, which justifies the analysis of moderating variables carried out. This analysis reveals that the variables associated with teachers have a greater influence in those countries with a lower Human Development Index (HDI). It also shows how the influence of teacher characteristics and competencies on performance varies according to the curriculum area –with a larger average effect size in foreign languages– and to the statistic from which the effect size is estimated –with a higher mean effect size for studies that provide differences between measures or correlations–. Finally, an interesting finding of this study is that articles published in journals that do not have an impact factor in either Journal Citation Reports (JCR) or Scimago Journal & Country Rank (SJR) tend to report higher effect sizes.

Ahmad, S., Hussain, C. A., Ayub, A., Zaheer, M. & Batool, A. (2017). Relationship of Classroom Management Strategies with Academic Performance of Students at College Level. Bulletin of Education & Research, 39(2), 239-249. Aloe, A. M. & Becker, B. J. (2009). Teacher verbal ability and school outcomes: where is the evidence? Educational Researcher, 38(8), 612-624. https://doi.org/10.3102/0013189X09353939 Blanco-Blanco, Á., López Martín, E. & Ruiz de Miguel, C. (2014). Aportaciones de los modelos jerárquico-lineales multivariados a la investigación educativa sobre el rendimiento. Un ejemplo con datos del alumnado español en PISA 2009. Revista de Educación, 365, 22-49. https://doi.org/10.4438/1988-592X-RE-2014-365-267 Cabrera, J. M. & Webbink, D. (2018). Do higher salaries yield better teachers and better student outcomes? MPRA, 86972. Campbell, P. F., Nishio, M., Smith, T. M., Clark, L. M., Conant, D. L., Rust, A. H., ... & Choi, Y. (2014). The relationship between teachers' mathematical content and pedagogical knowledge, teachers' perceptions, and student achievement. Journal for Research in Mathematics Education, 45(4), 419-459. https://doi.org/10.5951/jresematheduc.45.4.0419 Cohen, J. (1992). A power primer. Psychological bulletin, 112(1), 155. Coleman, J. S., Campbell, E. Q., Hobson, C. J., McPartland, J., Mood, A. M., Weinfeld, F. D. & York, R. L. (1966). Equality of educational opportunity (2 vols.). Washington, DC: US Government Printing Office. Escudero, T. (2019). Evaluación del profesorado como camino directo hacia la mejora de la calidad educativa. Revista de Investigación Educativa, 37(1), 15-37. doi: 10.6018/rie.37.1.342521 Glewwe, P. W., Hanushek, E. A., Humpage, S. D. & Ravina, R. (2011). School resources and educational outcomes in developing countries: A review of the literature from. National Bureau of Economic Research, 17554. Hanushek, E. A. & Woessmann, L. (2017). School resources and student achievement: A review of cross-country economic research. En M. Rosén, K. Yang Hansen, y U. Wolff (Ed.), Cognitive Abilities and Educational Outcomes (pp. 149-171). Springer, Cham. Harris, D. N. & Sass, T. R. (2011). Teacher training, teacher quality and student achievement. Journal of Public Economics, 95(7-8), 798-812. https://doi.org/10.1016/j.jpubeco.2010.11.009 Muijs, D. & Reynolds, D. (2017). Effective teaching: Evidence and practice. Thousand Oaks, CA: Sage. Murillo, F. J. (2016). Hacia un modelo de eficacia escolar. Estudio multinivel sobre los factores de eficacia de las escuelas españolas. REICE. Revista Iberoamericana sobre Calidad, Eficacia y Cambio en Educación, 6(1), 4-28 Wayne, A. J., & Youngs, P. (2003). Teacher Characteristics and Student Achievement Gains: A Review. Review of Educational Research, 73(1), 89–122. doi:10.3102/00346543073001089