This study investigated whether Chapter 1 middle school students showed more achievement gain when delivery of the pull-out supplementary reading or mathematics instruction was "massed" in time blocks or "distributed" weekly across the school year. All students in one Middle School Chapter 1 Learning Center program participated in the study. Approximately 250 students in supplemental reading and 260 students in supplemental math were randomly assigned to one of three delivery schedules for receiving Chapter 1 services throughout the school year. The Learning Center had four Chapter 1 teachers and four Chapter 1 assistants (two of each for both reading and mathematics). Analysis of the end-of-year California Achievement Tests (CAT) total reading scores, using fall achievement scores as a covariate, showed a marginally significant group effect favoring the once-per-week delivery schedule. A similar analysis of CAT total math scores showed no significant differences across the delivery schedules, although the once-per-week group did have the highest posttest mean. Two figures provide reading and mathematics results by group and by grade. (Author/TJH)