Empirical results are consistent with the hypothesis that socioeconomic factors contribute to initial disparities in performance that are perpetuated by demoralizing grading, testing, and grouping practices throughout the K-12 years. The hypothesis may explain why the achievement gap increases after children enter the school system, why Black students lose ground within schools and within classrooms, why value-added modeling (VAM) estimates of teacher performance are unstable from year to year, why Rothstein found that VAM estimates of teacher performance predict prior student performance, why VAM estimates of teacher performance predict gains in student achievement, and why persistent sorting may account for the Gates Foundation's Measures of Effective Teaching (MET) results despite random assignment of class rosters to teachers.