Four types of control groups are commonly used in cognitive manipulation studies: (1) no-treatment; (2) practice with own methods; (3) practice and training with competing treatments; and (4) practice and training with irrelevant treatments. There are problems associated with the use of each group as a baseline for identifying the "true" treatment effect. A general, two-step control procedure was advocated in which the researcher first identifies the most appropriate control group for a given context and then supplements this experimental control with statistical control. In reference to the latter controls, procedures were presented for developing a task-specific index as a covariable to be employed with a suitable measure of verbal aptitude in a multiple analysis of covariance. The procedure was demonstrated on data from a quasi-experimental design in which it was shown that three different conclusions were possible, depending upon the control procedures employed. The converging operations obtained from the multivariate approach to the data analyses supported the results from the two-step control procedure. (Author/RD)