PSAT Reading & Writing Question of the Day

Adolescents experience a shift in circadian rhythms that makes it difficult for them to fall asleep early and wake before dawn. Building on this biology, an education researcher argues that high schools should move first periods later in the morning. According to the researcher, doing so would improve average academic performance because students would obtain more sleep aligned with their internal clocks; the benefit, the researcher adds, should appear even if funding levels and course offerings remain unchanged. Skeptics counter that any gains credited to later start times may simply reflect other reforms adopted at the same time, such as expanded tutoring or new grading policies, or merely students' perception that they feel more alert. The researcher maintains that only controlled comparisons can decisively show whether later start times, independent of other factors, cause measurable improvements in grades.

Which finding, if true, would most directly support the researcher's claim?