My kids’ schools (elementary and middle school) generally have two, one usually involving magazines and a second one involving wrapping paper. However, their extracurricular school programs may have more. I know when the elementary school was brand-spang new they added in a third fundraiser (a sponsored walkathon) in order to buy playground equipment such as basketballs and jump ropes.
My daughter is now in high school and is active in sports and several clubs so there seems to be a fundraiser every time I turn around. She has sold cookie dough, croissants, frozen pies, cases of soda, homemade tamales, tee-shirts, and candy bars, and has participated in one car wash so far. This is mostly to cover using charter buses instead of “yellow dogs” (school buses) for the 2 1/2 hour trips to San Antonio for games, but also supports the French Honor Society and Christian Athletes.
I do think that for an established public elementary school that one or two a year is plenty. However, the local parochial schools seem to have about one a month.