When I first criticized the use of SGPs for teacher evaluation in New Jersey, the creator of the Colorado Growth Model responded with the following statement:
Unfortunately Professor Baker conflates the data (i.e. the measure) with the use. A primary purpose in the development of the Colorado Growth Model (Student Growth Percentiles/SGPs) was to distinguish the measure from the use: To separate the description of student progress (the SGP) from the attribution of responsibility for that progress.
Let’s parse this statement one more time. The goal, of the SGP approach, as applied in the Colorado Growth Model and subsequently in other states is to:
…separate the description of student progress (the SGP) from the attribution of responsibility for that progress.
To evaluate the effectiveness of a teacher on influencing student progress, one must certainly be able to attribute responsibility for that progress to the teacher. If SGP’s aren’t designed to attribute that responsibility, then they aren’t designed for evaluating teacher effectiveness, and thus aren’t a valid factor for determining whether a teacher should have his/her tenure revoked on the basis of their ineffectiveness.
It’s just that simple!
Employment lawyers, save the quote and link above for cross examination of Dr. Betebenner when teachers start losing their tenure status and/or are dismissed primarily on the basis of his measures – which by his own recognition – are not designed to attribute responsibility for student growth to them (the teachers) or any other home, school or classroom factor that may be affecting that growth.
(Reiterating again that while value added models do attempt to isolate teacher effect, they just don’t do a very good job at it).