The all-girls schools where I grew up (Louisville, KY) have their senior proms right before Christmas. Supposedly had something to do with military leave, but I’m pretty sure that’s apocryphal.
Sometime between mid-April and mid-May. It was usually done before final exams at my school so we could stop worrying about dates and dresses in time to study.
My prom was in may on the 15th to be exact. My sister schools around me were also in may, a few possibly in April. There usually held within those two months.
Usually in April in our school district. Last year they made the mistake of scheduling it during Passover and cut out a lot of students because it was a religious holiday.