In NFL fandom, Football Outsiders's Defense-adjusted Value Over Average (DVOA), is perhaps the best-regarded predictive model of results. In a shoot-out on /r/nfl last year, it outdid ~20 other ratings and rankings in predicting outcomes. One can only imagine that if predicting NFL games were as politicized as school outcomes, there'd be a powerful lobby claiming DVOA "doesn't make a lot of sense".

You're right, this particular model might be bad. But something along these lines will be good, inasmuch as correctly approximately evaluating a teacher's effect on outcomes is good. Science always wins.