The current study evaluates effects of teaching factors and extended day programs regarding both average achievement and socioeconomic achievement gaps. Analyses are based on data from the National Educational Panel Study in Germany. The sample comprises 1523 students in 120 classes in 71 secondary schools. The investigation period covers fifth grade to seventh grade. The dependent variable is mathematics achievement. Data are analyzed using intercept-and-slope-as-outcome models. Analyzes on teaching factors reveal that classroom management and cognitive activation increase average achievement. Forming heterogenous groups within the classroom reduces socioeconomic achievement gaps. Analyzes on extended day programs reveal that tutoring reduces socioeconomic achievement gaps. Homework supervision reduces average achievement and increases socioeconomic achievement gaps. Enrichment programs increase socioeconomic achievement gaps. Implications for research, policy and practice are drawn.