Thirteen high schools, recruited through a series of presentations
to educators or brief phone meetings, agreed to
participate and provide participating students’ academic
records. The schools were located in the eastern, western,
and southwestern United States. Eight were public schools,
four were charter schools, and one was a private school.
They varied widely in socioeconomic characteristics:
In
five schools, almost no students received free or reduced
lunch because of low household income; in six, more
than half of students did (see Table 1).
To maximize external validity and power, we sought
to include as many students as possible in the study.
Consequently, we permitted all interested schools to take
part provided that they agreed to try to enroll 100 or
more students and to provide academic outcomes for
participating students (not all schools reached this benchmark).
Our analyses focus on the 1,594 students for
whom both preintervention and postintervention semester
grades were available.