Which preposition to use with prep

on Occurrences 2%

DAWSON, ELMER A. Garry Grayson hitting the line; or, Stanley Prep on a new gridiron, by Elmer A. Dawson, pseud. of Edward Stratemeyer.

after Occurrences 1%

Besides, we aren't idle, we work hard at lessons all the morning, and we have half an hour's prep after tea.

Which preposition to use with  prep