Ready for the Grave (1990)

Though he is in his twenties, with a wife and children, the sociologist in this film is sent to study an aspect of the lives of high-school students, and must go undercover to do it. At first he is skittish about his role, but soon he discovers how much fun it is, and delights in the ability to win the attention of attractive girls. Meanwhile, his real family is not getting to see much of him, and conflicts arise.