That's a tough question, since different areas have different dates for Spring Break. Some schools have theirs around Easter, while others have theirs before or after Easter. I think it's fair to say that probably the 2 weeks before and after Easter will probably be pretty busy. Don't let that scare you though...we've been to WDW on many Spring Breaks, and as long as you plan ahead, i.e. Fastpasses, dining reservations, you really won't be bothered by the crowds.