I think spring break can be March, all the way through April depending on the school, and location. Easter long weekend is also around the time you are thinking.....I was originally wanting the last week of March 2013, but have changed, on the advice of my TA to deparing the week of April 6th. I'm not sure if it is the same in Mexico - but she strongly urged us to stay away from the Easter weekend all together in the Dominican, as it is their biggest holiday, and not a great time to travel. What I did, to be safe, was I chose a hotel that specifically states on their website that they don't do student groups. I think they had an issue (through checking tripadvisor) with a group of Michigan Highschool students the first week of april a few years back,and so many people complained they eliminated student groups from booking. Happy planning!