Progress in the development of an intensive time-series design for use in classroom situations has raised several questions regarding the validity of the data obtained. One such question is related to the effect of frequency of testing upon the data. This study was designed to determine the presence of such an effect. Use of the design with eighth grade students studying a unit on crustal evolution indicated that the frequency of data collection did not adversely affect student attitudes toward the science class nor did it have any measurable effect upon class achievement data. The results of a previous study were also replicated, giving increased confidence in the validity of the data yielded by the intensive time-series design as used in these studies.