For one afternoon, the school fills with small businesses, and every one of them belongs to a student in grades 4 through 12. They built the product or sourced it, set the price, made the sign, and they are the ones who will talk you into buying.
Bands and performers play all afternoon, so there is somewhere to sit down with whatever you just bought. Come browse, ask them how they made it, and bring cash — not every booth can take cards.
Free to attend. No ticket needed.
Bring cash — most young sellers can't take cards.