When two groups, initially dissimilar, undergo different treatments, can subsequent differences be partitioned in such a way that the difference between the two treatments is unbiased? This is the central problem of this paper, and it is confronted by the examination of two levels of information using a Follow Through Evaluation. The first information level contains, in addition to outcome variables (achievement tests), information on child characteristics and family background. The second contains all the variables of the first plus three achievement tests given at an earlier time. Although many educators believe it is important to use a pretest to adjust posttest scores, closer inspection reveals that this process typically explains only a fraction of the variation on posttest scores. Even if pretests substantially explain variations on concurrent variables, this does not warrant the conclusion that treatment differences based on posttests will be altered by additional information. It is concluded that a multifaceted approach may reveal the analysis or analyses best suited for a particular question. (Author/BJG)