This would seem to involve independant, standardised testing to be held on all students, every year. Letting teachers, or even the school, evaluate students would obviously make it too easy for biases.
I will admit I'm in the UK, not the US, but we only do huge standardised tests every 3 years or so, as they are very disruptive.
That way, the best teachers would want to teach the low performers, because that's where the max bonuses would be.