Schools (or camps) sometimes make raffles for their students. If you "Daven well", you get a ticket to a raffle taking place in the afternoon.
Sometimes, for good reasons or not, the school decides that it wants a certain student to win (he's "trying hard", etc.) They arrange that his ticket number is on the top (or will lie what that number that got picked out was), and will "randomly" pick it out.
However they arrange it, is it permitted (let's say the kids don't realize. They're too little, so there's no "chinuch issues"). On one hand, the school owns the prizes and can give them out to whomever they want. On the other hand, they made a "contract" with the kids, so perhaps it's too late to back out then.
What's the halacha?