The evidence is clear: better teachers improve student outcomes, ranging from test scores to college attendance rates to career earnings. Federal policy has begun to catch up with these findings in its recent shift from an effort to ensure that all teachers have traditional credentials to policies intended to incentivize states to evaluate and…

Value-added measures of teacher effectiveness are the centerpiece of a national movement to evaluate, promote, compensate, and dismiss teachers based in part on their students' test results. Federal, state, and local policy-makers have adopted these methods en masse in recent years in an attempt to objectively quantify teaching effectiveness and…