Your post is so succinct, but each of the factors you outlined are important ones to consider. Another one I can think of is, what about students how hadn't previous taken the SAT before taking an SAT prep course, what happens with their scores? Is this claim adjusted for extreme outliers on either end of the spectrum? There are so many variables and factors that can impact the validity of this claim, and therefore, with the amount of information provided, it is impossible to state whether the statement is a biased one or unbiased.comment