K-6th, we had gym one day per week for 45 mins.  We also had a 30-minute recess ever day where we'd run around, play sports, etc. 7th-10th, we had gym class every day for 45 mins. 10th-12th, gym was an elective.  Most people skipped it because they didn't want to stink for the rest of the day (not enough time to shower & primp after class).