We caught him up to monkey tricks, trying to change his grade.
Мы поймали его на мошенничестве, пытающегося изменить свою оценку.
Definitions
The phrase '(someone) up to monkey tricks' means that a person is behaving mischievously, playfully causing trouble, or engaging in sneaky or naughty activities, often in a lighthearted or humorous way.