MS Carpool - Why Can't HS Students Walk to the MS Before MS Carpool?

This year, all HS students are picked up at the HS instead of walking to the MS to join their carpool. We identified a safety issue as HS students walking between cars in the MS carpool line increased the chance of a student getting struck by a vehicle in a moment of inattention. There was also concern about the number of HS students on the MS campus at carpool time and identifying who should and should not be on the MS campus.