Renee Moore of TeachMoore voices skepticism about statistical attempts, often key to performance-pay plans, to measure the "value added" by a particular teacher to a student's achievement level:
This concept denies the cumulative aspect of education. It ignores the truth that multiple factors impact the learning and retention of that learning among students. ...
Moreover, students develop and mature as learners over time. A student may have been introduced to a concept or skill in 6th grade, had it reinforced in different ways by different teachers over several years, then in 10th or 11th grade that concept [seemingly] suddenly took root and the student actually assumed ownership of the knowledge as evidenced by a deeper understanding and ability to apply the concept. Such "seeding" and "harvesting" occurs repeatedly over the course of any student's educational career. Which individual teacher would get the "credit" for these accomplishments?