What has worked with your teen and school or other "official" dinners?  We've not experienced Prom yet, but we now have a number of banquets.

For banquets, I've just worked with the organizer to make sure nothing there would hurt DS. He is only PN (and we've found also allergic to shrimp, but he's a vegetarian). He had a very important banquet last week.  There were no blatant peanuts on the menu, but I got the info to contact the caterer to talk specifics.

But being only PA is quite easy for a banquet!  (I also ate there with my sesame and shellfish allergies.)

For cast parties in middle school--these were huge events as we had a very, very good theatre program--I just became the president of the theatre boosters and planned the cast parties.    I also moved the DQ outing that they kids traditionally made after the first performance to McD's.  The manager would open up the play area for our kids.   

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But for dinners in general, I care that he is able to eat something. He doesn't have to be able to eat everything (his vegetarianism limits that anyway), but I want him to have a few things he is able to eat.  But I don't want things there that can kill him.  But it would take a lot of convincing to me for him to be able to eat dessert--even if the caterer says it's okay.  It's just not my comfort zone. So at these dinners, unless they have a bowl of fruit topped with cream or sugar, he wouldn't be eating dessert.