Recess, Homework, and Test Score Paradox

The principal reasons post hoc ergo propter hoc: recess increased, scores increased, therefore recess caused the increase. But several other changes occurred simultaneously-new reading curriculum, two additional tutors, and free breakfast. Any of these could have raised scores, and their effects may overlap. Without a control group or a way to isolate recess, the principal cannot conclude that recess was the cause. At most, the evidence is consistent with recess contributing.

A comparison group of similar schools that did not add recess but did make the same curriculum, tutoring, and breakfast changes. If those schools' scores rose less, the recess effect gains support. Alternatively, a within-school design comparing classes that received different amounts of recess while holding other changes constant, or a dose-response pattern (more recess, larger gains) would strengthen the causal claim. Random assignment to recess schedules would be strongest.

Overdetermined means more than one sufficient cause is present: the new curriculum, tutors, breakfast, and recess could each be enough to raise scores. If so, the observed increase does not tell us which cause operated, and the principal's conclusion that recess must be the cause is unwarranted. Recess could still be a contributing cause, but the evidence cannot single it out. The proper conclusion is that the increase is consistent with recess but not uniquely attributable to it.