As an educator and a mom, I'm always dissapointed when people want to move toward these watered down P.C. versions of holidays ("winter holiday" for example).
When I was a kid, I grew up on the east coast and had a reasonable number of Jewish kids in class with me. Instead of not doing christmas, we just did Christmas AND Hannukah stuff. I looooved playing dreidel, learning about the holidays they celebrated, etc. We wrote out lists for Santa, made christmas ornaments, made dreidels, decorated menorahs, etc. I suppose if Kwaanza had existed back then (or anyone in our class celebrated that) we would have done that as well. In cases where a teacher might not know enough about Judaism, one of the moms would come in and teach us.
I guess I just wonder why it can't be "both/and" instead of "none." (not directed at the OP, but just in general).
No one in public school is talking about religious aspects, but simply joining in the children's excitement about wearing costumes, getting candy, and having fun.
I find as an educator in Texas, many of my peers know anything about Judaism. Its kind of sad. I think we are missing something by not sharing all of our cultural traditions with eachother.
I fully support any parent's right to exclude their child from said activities, but I think its really better to not make a stink. OP, your approach sounds entirely reasonable to me. And if it were me (and I didn't think my kid would be too dissapointed with leaving after witnessing the pre-party hype), I'd take him in the morning so he was counted for attendance and getting the day time instruction. Lunch and ice cream sounds fun!
For the record, I'm buddhist. But my family has Christmas and Halloween because we enjoy them as a cultural tradition. Also, Christmas is a great time to connect with family, be generous, etc. I don't think it has to be religious for everyone (although I know Christians often are upset by this notion).
Also, my daughter has a dairy intolerance and often has to "miss out" on treats for birthdays, cake, pizza parties. I just send an alternative "treat." I would never dream of asking the school to stop having dairy for all children, because my daughter cannot.
Best wishes to the OP. I know its hard having to exclude your child from something the masses are doing (as I have felt sad sometimes with the dairy issue for us). Different, but I think a similar feeling. We don't want our kids to miss anything, but want to keep our family's values/needs intact.