High performing students ≠ Highly effective teacher

Sheri Lederman may, in fact, be an excellent teacher. But the fact that her fourth-grade class performed well above the New York state average on both the math and English tests is not evidence of her effectiveness. That’s because overall scores such as these have long been known to be more a measure of the quality of the students a teacher is assigned than the actual effectiveness of that teacher. As such, such scores should never be used to evaluate teachers.

Why would this be the case? Let me give you an example. Say Teacher A is assigned a remedial class where just 15 percent of students pass the state test, while Teacher B is assigned to a gifted class where 70 percent of the students pass the state test. However, 70 percent of Teacher A’s students made more than a year’s worth of growth, while just 15 percent of Teacher B’s students did so as well. Which teacher do you think is more effective?

Based on these test scores alone, Teacher A would be considered the more effective teacher since the amount of growth individual students make from one year to the next is more indicative of a teacher’s true effectiveness than scores for individual students at one point in time. So, the fact that Lederman’s students scored above the state average is basically meaningless when it comes to evaluating her effectiveness.

What needs to be known is how much growth her students made over the past year and how that compares to other teachers. But simply comparing the growth Lederman’s students made to the state average isn’t a very accurate measure of a teacher’s effectiveness either since a student’s prior achievement and background can influence how much growth they make in a given year. Such differences need to be accounted for before growth measures can be used to evaluate teachers.

In fact, New York state does account for such student differences when evaluating teachers based on student test scores—including Lederman. The statistical term for including such measures is called the Value-Added Model or VAM which simply determines if a teacher’s students made more, less, or similar academic gains had those same students been taught by an average teacher.

In 2014, the statistics show that Lederman’s students, for the most part, would have made greater academic gains if they had an average teacher. This was not the case for her previous class. So one must ask why the difference? How can a teacher’s performance change so much from year to year?

The answer is VAM’s are not perfect measures of a teacher’s effectiveness, so results may vary from year to year even if the teacher’s actual performance hadn’t changed. Keep in mind, while VAM’s get criticized for their inaccuracy, other measures including classroom observations are in many cases less accurate measures of a teacher’s effectiveness. However, research shows combining student growth measures along with other measures of teacher effectiveness– like classroom observations—provides a pretty accurate measure of a teacher’s true effectiveness.

Are teacher evaluations perfect? No, which is why decisions about individual teachers should be made based on multiple evaluations, not a single one. Even then, results should be used to inform personnel decisions not mandate specific actions. Those decisions should be left in the hands of school and district leaders who know what is best for their students. For Lederman, those who know her best consider her a good teacher despite her last evaluation. The question is: would their opinion change if she continues to receive poor evaluations? Time will only tell. – Jim Hull

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