What has worked for us is getting to know his classmates and their parents, and nurturing friendships (at the kid level and the parent level) throughout the year, whether it’s chatting in the schoolyard at drop-off/pick-up, sharing useful parenting info, putting them on the Christmas card list, etc. I host a holiday party every year, a big casual drop-in for friends, family, neighbours, etc. and it’s a great way to get to know people better, and an excuse to invite people we don’t know well to deepen the connection. For that party, I will give my kid a few paper invites to hand out. But for birthday parties where you really need to know who’s coming, I never do paper invites – kids will lose them before they get home anyway. Email or text the parents directly, follow-up for RSVPs as needed. Send a reminder the day before with a “looking forward to seeing you tomorrow” type of message. If you use a free online service like eVite, it will send out reminders automatically.