You can probably find resorts that are far less 'spring break' if you have a look - for example, 'couple only' resorts may attract less teenage interest. Teenagers generally want a) cheap and b) lots of activity, so if you pick a quieter island / resort, at the higher end of the price point, you would probably avoid them en masse. I'd probably stick to Caribbean / Mexico (short flight) rather than go long haul for a week. I've done Thailand in coach, and I wasn't a particulaly happy bunny (and certainly needed a couple of days to adjust, which seems a bit of a waste on a week's vacation).