Should the grade-level a student is in be based entirely on how old he is or at least partially on how skilled he is? This is the fundamental question underlying the debate over social promotion — the practice of moving students to the next grade regardless of whether they have acquired the minimal skills covered in the previous grade. Advocates of social promotion suggest that it is best to group students by age rather than by skill. Students who are held back a grade are separated from their age-peers and, the argument goes, this social disruption harms them academically. Opponents of social promotion favor requiring students to demonstrate minimal skills on a standardized test before they receive automatic promotion to the next grade.
Until now the bulk of the research favored social promotion. Most studies found that students who were retained tended to fare less well academically than demographically similar students who were promoted. The problem with this previous research is that it was never entirely clear whether retained students did worse because they were retained or because whatever caused them to be retained led to worse outcomes. This is especially a problem because these previous studies examined retention based on educator discretion. If teachers decide that one student should be retained while another demographically similar student should be promoted, they probably know something about those students that suggests that the promoted student has better prospects than the retained student. When researchers match students on recorded demographic factors they cannot observe or control statistically for what a teacher saw that led that teacher to promote one student while retaining the other.