It's hard to know what the system really does because the article really doesn't explain it. I think what you're describing is Cross Validation[1]. It would w

It's hard to know what the system really does because the article really doesn't explain it. I think what you're describing is Cross Validation[1]. It would work if they are predicting performance, but it sounds like the VAM system might be trying to figure out what a hypothetical "average" teacher would have achieved with the same students and comparing that the actual teacher's performance. This is basically trying to predict how the students will do independent of the teacher, but without such a teacher there is no real way to validate the model. Perhaps if they examined students across all teachers. The system may ultimately be more about comparing teachers to each other and not about actually determining the value provided by an individual teacher. 1: http://en.wikipedia.org/wiki/Cross-validation_(statistics) http://en.wikipedia.org/wiki/Cross-validation_(statistics)