This is an long raffle fundraiser, but very profitable and well received.
You set up a calendar which would be printed right on your raffle ticket. Then on that calendar you have the payments which get paid out everyday for the next 90 days. You determine what the prize amounts are.
Your kids sell the tickets and all tickets go into a container. You pull each day for 90 days. However you can state right on the ticket that you will pull each week of tickets every Monday morning.
For example:
200 students sell 10 tickets each at $10 each. (these are plug numbers, you can change the amount of tickets sold and the price)*
You bring in $20,000 gross.
You pay out $8,000 in prizes, license fees, printing fees etc.
The rest is yours.
*keeping the price of the ticket reasonable is beneficial. Those who do not know the organization are more likely to purchase if the price is low.
Each ticket can win more than once. So once a ticket wins, it goes right back in. This is a selling point, people like the idea that they can win more than once by only making one ticket purchase.
Be sure to talk to your state. You do need a license and there are state rules. If you need an example of a ticket, I will email an example to you.
Good luck.