The validity and reliability of the Technological Pedagogical Content Knowledge (TPACK) framework to measure the extent to which teachers can teach with technology, hinges on the ability to aggregate results across empirical studies. We synthesized mean difference effect sizes resulting from university classroom studies, which used a survey of preservice teacher knowledge of teaching with technology (TKTT) using confidence intervals (CIs). We then characterized the mean effect sizes for the influence of classroom instruction on preservice teacher TPACK by graphing CIs across studies from 2009 until 2011. The results present approximations of TPACK population parameters as well as implications for researchers and teacher educators.