My son's elementary school did class plates. Each classroom had a mom that volunteered to do the plate and then they came up with a theme... animals, alphabet, etc. Each student put their thumbprint on the plate and decorated according to the theme. All the plates were taken to a local kiln for final preparation. The plates were usually very cute, especially if a creative mom was involved! Each sold for over $100 at the silent auction. Often, parents would buy the plate and then give it to the teacher as a gift.
When my girls went to a private school, something the Kindergartners did was put a footprint on a toy box (with the help of parent volunteers) then their name was written next to their print.
LOVE the chair idea! Did you get unfinished furniture chairs, say at Michaels or something? Sounds great. What kind of marks did the kids put on the chairs?
We had each class paint a chair. The chairs were donated or garage sale items. The art teacher helped and had each student make their mark on the chair. Some chairs had themes, some were just a mismash of everything. We had a silent auction total raised was 2,000 dollars. The chairs made $600 themselves. Many of the teachers wanted their own chairs and fought tooth and nail to get them. It was alot of fun, but alot of work for the art teacher, so would recommend alot of help from parents during classes to get the painting done.