Also, remember that two 50-minute classes had an average of 5 minutes of startup time (e.g., taking attendance, catching up absent students, passing back papers) for each period; that is halved automatically by block scheduling, and the same is true for the end-of-class time spent explaining homework. To say that 10 minutes were lost by changing two 50-minute periods for one 90-minute period is not accurate when you adjust for less administrative work. Also subtract the average amount of time spent reviewing for a typical day on a traditional schedule because there will be that much less time needed for review when two periods are combined into one. When those adjustments are made, there is little lost time.