exhaustivly investigate any organization before you seriously consider sending your child on travel with them.
i have concerns with some organizations because when i taught i received solicitations to make reccommendations of students where it was totaly left to my discretion as to the criteria, and there were incentives offered to me if i successfully got so many to pay up and travel (as in free travel for myself). i never chose to work with these groups but i knew of teachers who did referrals purely based on who they felt they could get to pay in order to meet their quota for free travel (so some travelers may not be the best traveling companions for your kids).
dd (15) began receiving solicitations from people to people (ptp) begining in preschool. we immediatly knew, despite what the letters said about it being based on an academic referal

rotfl: at 3 years old) it was from a mailing list purchased by ptp because her name was mispelled in the same unique manner as was done on a magazine subscription a relative purchased. in middle school 2 girls from the private school dd went to were solicited and particpated in a ptp trip, their teacher who was also principal were flabbergasted that the letters said it was based on an academic referral b/c the school had a policy barring any such interaction with these groups. the 2 girls that went also both had lengthy juvinile criminal records that would have seemed to preclude their participation but apparantly ptp had no issue so long as their parent's check cleared.
ptp is local to us-their headquarters are in spokane. i can't speak to what they tell people their staff has in the way of education and training, but they routinely solicit trip chaperones and other staff that work face to face with the kids through the 'unskilled labor' and 'telemarketing' sections of the classifieds (apparantly a trip chaparone only needs a highschool diploma, a clean criminal background and must be able to pass a drug test

).
a friend (now retired) worked for many years in student international travel. his job was being the person who handled emergencies and urgent situations. he cautions parents that are looking into international (and to some extent national) travel programs for students to QUESTION, QUESTION, QUESTION and then ask for examples of how any organization deals with the 'what if' situations that can and do come up. don't assume that if an organization says they have a plan in place they do, and ask what the plan is (they should have it in writing). ask them if they have staff local to you that speaks the language of the country your child will be traveling to, and if they have 24 hour emergency access for both the student and the parent to the local staff (difficult at best with differences in times around the world if the officials/med providers your child needs to see are only available during that country's 9-5 which ends up being the u.s.'s overnite hours). local staff that speaks the language can facilitate a 3 way call between a parent and a vital person to speak with in another country, absent that you may end up trying to juggle finding interpreters and facilitating conference calls in regions where technology does'nt lend itself to the process. finaly he reccommends that no matter what a group says about the credentials of their staff who will travel with the students-ask to see verification (some will claim education and certification is held by staff but either it's not or it's all in-house done by noone with any particular professional training/education in the subject matter).