This is one of those things where I remember maddeningly little detail, but I keep running into questions on the site that reminds me of it. I read it somewhere in the 90s as a paperback, probably from my local library in Kentucky. One of the bits that has stuck for me is that the cover had a black metal robot, inhuman-looking, I think with more than two arms, which had one of kids held up in the air (either by his neck or the front of his uniform) while the others attacked around it. The kids were all dressed alike. I vaguely remember that it was a sort of military feel to it and the kids weren't there entirely by choice, having been picked out because they were extremely intelligent.
The other bit that I vaguely remember was that one of the characters (I think it might have been one of the teachers, not one of the kids) had undergone some sort of treatment, whether it was an implant or the result of hypnosis, that removed compassion and emotion from him, allowing him to be a more effective fighter. I have this lingering memory that he got attacked and was choked to unconsciousness, and I remember thinking it was tremendously unfair that, with his special ability, he was taken out like that.
If I remember any other details, I'll post them here, but that's all that's coming to mind.