well depending on where you are its probably still early in the high school season and he has time to pr. but he should probably be doing some type of speed work at least once a week. It doesn't need to be much under 400m. I don't usually do short speed work until i have the base sprint endurance that is needed to finish the 400m. It also depends on how much speed your son already has. If he has good speed in the 100 and 200 but has trouble finishing the 400m then the longer workouts are probably best.
