While «it will take time to develop richer and more
sophisticated measures of teacher effectiveness,» Haycock writes, «until then policymakers should use a combination of the best available measures.»
There are a number
of reasons: 1) student achievement probably wasn't used as the
measure of teacher effectiveness; 2) before the advent
of the modern computer, in the mid-1960s, some
of the more
sophisticated analyses were not feasible; 3) the structure and makeup
of schools change, making the findings less applicable to the current situation; 4) most important, older studies may not control for critical variables, such as students» backgrounds or past achievement.