You can easily invite a smaller number of just the kids he is closest with. You do not have to invite the whole class, I think that rule is insane. It's just plain good manners though to not bring invitiations to school if you don't offer one to everyone. Whatever you do, don't discreetly put invitations in the kids cubbies if you aren't inviting the whole class, thinking just parents will get to them. I was once picking up my daughter and a friend from preschool. Guess what? When I emptied their cubbies of artwork, mittens, etc, I found an invitation in my daughter's friend's cubbie, but not in my daughters. No, it wasn't missing, the girl had only invited 6 or 8 girls from the class, and her Mom slipped them in before dismissal time. I actually watched her do this, so I know. So then I had to try to sneak this bright purple envelope in to the friend's Mom when I dropped her off, but the little girl still saw it and then so did my daughter. Not cool. I totally did NOT expect her to invite the whole class, now was I upset she did not invite my daughter. I personally prefer small parties, so I get that totally, but I WAS mad at her for being too lazy to actually track down the addresses and mail her invitations out.