I agree with Serendipity. We also do it this way. Have to have a paper trail just in case it was ever brought up then you can show the parents exactly what their teacher purchased.
When we give out vouchers to the teachers for their classroom that is how we do it. They make the purchase, submit a receipt and then we give them the money back. The reason this is done is to ensure that the teachers spend the money on items for the classroom. It is done this way to keep everyone honest. Otherwise whether it is from a donation or not you have no way of knowing whether the teacher spnet the money on themselves or bought stuff for the classroom. In a perfect world no one steals and everyone does the right thing. Unfortunately we do not live in a perfect world. While most teachers are honest and will do the right thing with the money this protects the money from the dishonest person.
The PTO at our school recently held a silent auction of baskets provided by individual classrooms. The idea was that the students (parents) would make a theme basket that would be auctioned off and the classroom would receive the proceeds from the auction. Now that the auction is over, the PTO will not give the teacher's the money to spend in the classroom; they want the money spent first , have receipts returned and then the teacher will be reimbursed. Are there are any rules about this type of donation? Because this money came from donations provided by parents, are receipts even required? Any help would be great!