Is there a possibility that a teacher who doesn't produce the best results academically can nonetheless provide valuable and life-altering services to the kids they teach? I had horrible grades in public school because I was a little shithead... But in retrospect, there were two teachers who had a profound impact on my life, who taught me social skills that in turn allowed other teachers to get the job of teaching done.
Hell, half the value of public school is socializing kids. It isn't just about learning material. I see nothing wrong with rewarding teachers who go above and beyond to positively impact a students life in ways that aren't strictly academic. What about a teacher that gets a kid out of an abusive home? Who volunteers hundreds of hours every year running extracurricular programs? Who manages to tame a f**k up kid even if they don't learn the material?