Here in Texas, Spring Break, for all school levels is the week of March 13. All resort destinations in Mexico will be swamped by students and US families.
The only silver lining is I always factor in an extra day on both ends so I can
volunteer my seat as the airlines overbook by alot. Seats connecting through
IAH or DFW needed to be purchsed a month or more ago. If you don't require beach there many quiet & interesting destinations. Eg. Oaxaca, Michoacan, Guanajuato, Puebla, Jalapa, etc. For beach destinations at that time it's a tough call. The very fine Camino Real, Puerto Vallarta has a quiet beach all it's own and is 5km removed from town.