Most teachers like the shorter classes. The teacher-pupil ratio has dropped in some required classes. There is less time for lab classes. Two schedules run concurrently. Students could take one class a day for a 210 minute block or students could take two 100 minute blocks a day.
Time is the culprit.
Music enrollments have held steady in schools with seven or more periods in the school day but have dropped off in schools with six or fewer periods, according to the results of a 1987 survey of M.E.N.C. members. The school day should include at least seven or eight periods. A school attitude survey revealed contradictory perceptions. Teachers felt more stress by having an extra preparation and only having 45 minutes in class to cover material. The student attitude was more positive.