So many birthday party threads, why not add to it?

Since school started in September, my eldest has received 3 classmate birthday invitations. Two conflicted with weekend lessons but we compromised by allowing her to leave both lessons a little earlier. We only made these exceptions since she is new to the school and playing catch-up getting to know the kids in her class. But we really don't want to set an expectation that social activities will be a priority. We already explained to her why we were compromising, and that we wouldn't always make these exceptions in the future.

Can any parents relate, especially ones with school-aged kids? One friend of my daughter told her that she had to choose between two of the birthday invites as they both fell on the same weekend. I'm thinking maybe i can compromise 1-2 lessons per semester/term? Do you let your kids go to all the birthday parties? One weekend was crazy because we had a total of 4 birthday parties!