What do you do about behavior issues away from you?

I am feeling helpless here ... I just spent 30 minutes talking to my STBAS's kindergarten teacher. Apparently he has become extremely defiant lately ... won't listen, won't do his classwork. Today he spat on another kid's work. Then at lunch apparently he reached over and touched the boy next to him in the crotch. (I know I should probably freak out about that, but to be honest that part is the least of my concerns ... there is no SA in his past and I think it was completely innocent.) She said the huge increase in behaviors has been happening ever since coming back from the Thanksgiving break. I was flabbergasted because I haven't noticed anything like that at home. We are definitely having more problems with him not listening and having temper tantrums (as I posted about recently), but it's not as recent as this behavior at school and he isn't really defiant the way he is at school. At home he might not want to do something and he might kick a fuss but generally he will do it. So what do you do when you're not there and you can't intervene? obviously we will have a long talk with him and reinforce with him that he needs to listen to his teacher. I also asked his teacher to send home any work that he won't do in class, and he will have to complete all of that once he gets home. One of the big things that my STBAS needs is consistency. NO WAY can you say "no" at first to him and then say "Well, just this once" -- because then he will never take no for an answer again. However, it sounds like that his teacher has to "give in" because she has 20 other kids in the class and she doesn't have the luxury of standing there waiting him out. So I think he may feel that he can do whatever he wants because there are no real consequences. She says that really the only thing she can "take away" from him is recess, and he never seems to care about missing it. The teacher has had problems with him listening to her for awhile now but not on this scale. She was supposed to do a "color chart" for him (red = bad day, yellow = so-so day, green = good day, blue = awesome day) and send home each day what his status was and we would respond appropriately, but in the last two months she's only sent home a color status 3 times. So I am a little frustrated too on how I can do anything about his behavior at school when I don't even know anything about it until I get one of these phone calls. Help??? :confused: