I want to go to a warm spot with a beach & water activities with my daughter (high school senior) over her spring break. I definitely DO NOT want a place where the college/high school kids go to get rowdy, but would like somewhere that's a good value. Any suggestions? Thanks

Hola:
My suggestion would be the Melia Sol Club Cayo Largo, Cayo Largo del Sur, Cuba.
One of the Caribbean's best beaches, good activities (within the resort), very safe, and a tremendous spot for a vacation where R & R are a high priority. It's a small quite island, but that's the attraction.
More info at.....
http://www.cayolargodelsur.cu/
Enjoy yourself.
Steve

Playa Del Carmen, Mexico has beautiful beaches and lots of activities, but it isn't the "party hardy" that you'd find just down the road in Cancun. There are many US tour operators that have packages that would be a good value. (I've used MLT and Funjet before with much success on both.) I'd recommend an AI resort just for convenience with your daughter.

FORGET CUBA,ST JOHN,NO CROWDS EVER EXCEPT AT TRUNK BAY WHEN CRUISE SHIP PIGS INVADE SHORES TWICE A AWEEK ,AND EVEN THEN IT AINT THAT BAD.

Cayman Islands.... and yes, you can get good values...