This study assessed the hypothesis that preservice teachers who were required to assemble a portfolio assessment would report greater scores on professionalism as measured by The Student Teaching Reflection Survey (STRS) (Robichaux, 2001) than preservice teachers who were not required to assemble a portfolio assessment. Results from a sample of 510 preservice teachers (232 nonportfolios and 278 portfolios) supported the hypothesis. Assembling a professional portfolio appears to develop more reflective practitioners, which in turn leads to the development of a more effective educator capable of handling the complexities of the teaching profession.