Grade-by-grade testing and graduation tests actually increase schooldropouts. A Harvard University study found that students in the bottom 10 percent of achievement were 33 percent more likely to drop out of school in states with graduation tests.The National Research Council found that low-performing elementary and secondary school students who are held back do less well academically, are much worse off socially, and are far likelier to drop out than equally weak students who are promoted. Retention in grade is the single strongest predictor of which students will drop outstronger even than parental income or mother's education level.