To facilitate cost effective bus schedules, middle school classes begin one hour later than high school classes in the Fort Worth Independent School District, Texas. This study investigated whether middle school students were adversely affected, in terms of grades and classroom performance, by having the class day extended to 4 p.m. High schools were included in the study to determine the effect of time of day on last period students. Grades were collected from sets (a morning class and a comparable afternoon class taught by the same teacher) of fall, 1983, English or math classes. Classroom observations were made in the spring. Findings indicated that: (1) grades were not significantly higher in morning classes. Middle School student grades were higher in last period classes; (2) time on task was not significantly higher in the morning; (3) noise and activity levels were higher in last period classes, but this only affected student performance when teacher management skills were weak; and (4) the later start time caused individual student problems and scheduling difficulties for school personnel. Since middle school student achievement was not affected by the later time for last period classes, no schedule changes were recommended except for scheduling extra-curricular activities during before school hours when feasible. Appended are teacher and staff comments and a table showing distribution of student grades for Fall, 1983, by subject, level, and teacher for first and last period classes. (BS)