Value-added measures of teacher effectiveness have drawn words and ink from people who both support and oppose it, but the latest blow to those who wish to do away with the controversial evaluation approach could be a new study out of the Manhattan Institute of Policy Research. The report, authored by Marcus Winters, finds that a statistical analysis of student test scores can rate teacher quality with high degree of accuracy.

Value-added modeling uses test scores, or other objective student achievement metrics, to determine how much the quality of teaching instruction contribute to academic outcomes. During his research, Winters found that while VAM does not form a completely fool-proof way of assessing teachers, the right models are effective enough in identifying teacher contribution to student achievement that they should play a substantial part in decisions regarding teacher tenure. Tenure decisions made based on value-added analysis, concludes Winters, will ensure that only quality teachers remain in classrooms better than the current process where the granting of tenure is largely automatic.

Winters notes that current teacher tenure policies do little to remove poor teachers, who increase students’ rates of teen pregnancy, reduce the changes their students will attend college, and subtract as much as a grade level of learning from pupils in one school year.

“Transforming Tenure: Using Value-added Modeling to Identify Ineffective Teachers” analyzes data from Florida Public schools to conclude that a third-year teacher’s VAM score reliably predicts his or her fifth-year teaching success. He notes that researchers have found similar results using data from North Carolina.

Winters’ conclusions also confirm previous studies which found that teachers who obtain graduate degrees perform no better than their peers with only undergraduate educations.

In his paper, Winters also makes suggestions on how his findings should shape education policy on both local and state level. For example, Winters contends that granting tenure shouldn’t bring to an end all meaningful assessment of teacher quality. On the contrary, even tenured teachers should be subject to periodic reevaluation, with loss of tenure being one possible consequence of poor performance.

He evaluates the outcomes of different ways to use VAM in tenure policy, concluding that removing teachers who consistently perform poorly—each year for, perhaps, a period of three years—mitigates the possibility for removing too quickly teachers who have simply had a bad year or been subject to inaccurate assessment.

“VAM, when combined with other evaluation methods and well-designed policies, can and should be part of a reformed system that improves teacher quality and thus gives America’s public school pupils a better start in life,” he concludes.