We just always have because his father is Mike or Michael.
Well, DH met DS' teacher today and she was very nice but she REFUSES to call him Dave or David or Davey. She said that she only calls her kids by their first name and she doesn't use nicknames. I TOTALLY get not using nicknames...but David is part of his name. So DH said "Well, you could call him Michael David" and she asked if David was part of his first name, which its not...so she said no. She was going to call him Michael.
I mean, I don't think it'll cause serious issues with my son-we'll just explain it to him-but i can't guarantee he won't correct her for awhile. I mean, he'll do it respectfully (he'll be a mouthy brat to me but he's pretty good with manners around other people). I just think its such a strange thing for her to do.