330, Class-size effects, grade retention, and Welfare/I.I2 - Education and Research Institutions, J21, unobserved heterogeneity, secondary education, grade retention, unobserved heterogeneity, finite mixtures of normal distributions, treatment effects, class-size effects, Class-Size Effects, Secondary education, Grade retention, Treatment effects, Education, Unobserved heterogeneity, Unobserved Heterogeneity, secondary education, I2, Grade Retention, C36, C38, M50, [SHS.ECO] Humanities and Social Sciences/Economics and Finance, E32, class-size effects, JEL: I - Health, Applications of statistics to social sciences, JEL: C - Mathematical and Quantitative Methods/C.C2 - Single Equation Models • Single Variables/C.C2.C23 - Panel Data Models • Spatio-temporal Models, ddc:330, Treatment Effects, Factor analysis and principal components; correspondence analysis, treatment effects, [SHS.ECO]Humanities and Social Sciences/Economics and Finance, JEL: C - Mathematical and Quantitative Methods/C.C3 - Multiple or Simultaneous Equation Models • Multiple Variables/C.C3.C36 - Instrumental Variables (IV) Estimation, class-size effects C23, Secondary Education, Finite Mixtures of Normal Distributions, E24, finite mixtures of normal distributions, Finite mixtures of normal distributions, JEL: C - Mathematical and Quantitative Methods/C.C3 - Multiple or Simultaneous Equation Models • Multiple Variables/C.C3.C38 - Classification Methods • Cluster Analysis • Principal Components • Factor Models, C23, jel: jel:M50