I have a 15 year old nephew w/CF who also has B. Cepacia. And I have two daughters, both with CF, who do not. We keep the kids away from each other. The doctor says at least 3 feet away, but lately I have been wanting to keep them even further away. I am just too nervous about the whole thing. He has had B. Cepacia for 5 years. I do give him hugs and kisses when I see him, and have never been told that I can't by the CF doctor. All three kids see the same CF doctor, so he is definately aware of the close relationship and the situation we are in. I was told that I could not pass it to my girls. Although I have had others on this forum say that I can merely by having close contact with him. Maybe I have just been lucky so far, I don't know. Maybe he just hasn't coughed on me and got it on my clothes. Who knows. But I still hug and give him kisses. I don't go up hugging on him when he is in the middle of a coughing fit or anything.
If it were me, I would request that your son be able to see and become familiar with who this teacher is and vise versa, so that they do know to stay at least completely across the room from each other. My children (who were 2 and 3 when my nephew was dx with B. Cepacia) and my nephew (who was 10 when he started culturing it) have learned how to stay away from each other easily. As a matter of fact, my children have been taught to stay across the room from ANYONE with CF. There is another child with CF in our small school of only 150 students. If we are someplace, and they see Dalton (my nephew) touch something, like the remote control, they will not touch it. They will ask me or someone else in the family to turn the channel. We do the best we can with it and still be a family.
I think your son is okay, as long as he knows who to stay away from. When first explaining it to my girls we just told them that Dalton had a bad cold that they could catch and that it would make them really sick, and that explaination worked for years, and still does.