Secret Admirer (1985)

On the last day before summer vacations Michael receives a glowing, but anonymous, love-letter. He suspects, or better: hopes, it's from Deborah, the girl he's after since a while, but who dates college students only. However she shows him a cold shoulder again. So his and her best friend Toni advises him to write her an anonymous letter in return. However these letters get in the wrong hands and cause lots of confusion in their families, until it's revealed, who wrote which letter to whom.