My fourth grade classes have about 17 students. It really didn't take too long to do the testing, because once the student missed a single note, s/he had to stop and try again at a later date.

I also watched fingerings as the students were playing, then selected the kids who had been fingering accurately during group time. I would let two or three students play for me as the class was leaving - especially a student who was extremely shy in front of peers.

Occasionally, I would have to tell a student that we were out of time, but I would promise to audition him first at the next class. They never really complained about that.