Thanks again for all the comments.
I am operating on the assumption that the teacher could simply choose to not do the spring break trip. She could certainly just say, hey kids, have a great spring break, see you next week. Nobody is forcing her to offer this trip to the kids - at least that is my impression. I could be wrong about that.
What I think is going on is that the teacher got connected with the touring company who said to her that she could offer this trip, and the benefits to the kids would be a great, fun trip, and the benefit to her would be providing that fun and educational trip to the kids and her costs would be covered. Her mental math is probably:
+ kids get a fun trip
+ I get my dollar costs covered
- I have to advertise the trip to the kids
- I have to give up my spring break
- I have to be responsible for the kids
I doubt the teacher gets overtime. I believe she is a salaried employee.
@EastWestGal, it sounds like the exact same trip that my DD will be going on. What occurred to me in reading your response is that part of the lower value of the Disney part of the experience is that I took DD and DS to Disneyworld about two years ago, so she's already experienced the "magic" of the Disney parks. So I know she won't be impressed with that part of it.
@ivinsfan, what I mean is that it is not explicit that there are conflicting interests. If an annuity salesman says to me, "Hey, buy this fantastic annuity, it's good for you!" they are not also saying, "And by the way, out of that $100K check you're writing, $10K (or whatever) is going into my pocket as a sales commission!" Some people, including most here, would know about the commission. Some people wouldn't, and some would consider that these unaware people had been taken advantage of. Some people might want the annuity but think the commission is too high. To take it back to the trip, nowhere in any of the literature and nowhere in the teacher's email or comments does she say, "10% of the cost of your trip is going to defray my trip costs" and nowhere do we have the option of defraying more or less of her trip costs. If it said, even in tiny print at the bottom of the flyer, "As a way of compensation and appreciation for the teacher's efforts, 10% of your trip cost contributes to the teacher's trip costs. If you want to help more, just add a 'teacher supplement' to your payment and indicate it on your payment slip" I would feel much better about it.
I should add that I don't think the teacher is being malicious or sneaky about any of this. She is a great teacher and a sweet person. I think it is far more likely that she simply hasn't thought through or understood about the conflict of interest part of it.
Also, I'm about 95% sure at this point that DD will go on the trip. She already has plenty of money in her savings to pay her part, and her Mom and I are pretty much on board with her going (I am, anyway, not so sure about my ex).
I apparently haven't made it clear, but there is clearly a tour company involved which is acting like a travel agent of sorts. The teacher's role is to get as many students to attend the trip as possible, but I believe beyond that the tour company is handling all of the details - collecting payments, buying the plane tickets, setting up the buses, the meal vouchers, etc.
As for extra expenses, I suspect that the tour company handles all of the payments and arrangements behind the scenes. Transportation, hotels, and meals are provided, and if the kid wants a Mickey Mouse t-shirt or whatever, they are being told to plan on bringing their own pocket money for that sort of thing.