The four main approaches to measuring treatment effects in schools; raw gain, residual gain, covariance, and true scores; were compared. A simulation study showed true score analysis produced a large number of Type-I errors. When corrected for this error, this method showed the least power of the four. This outcome was clearly the result of the computational method which adds dependent variable information into the independent variable to form the true score. Covariance analysis was recommended, with reservation, as the method of choice. (Author/MV)