This study posits that instructional representations are viable assessment tools of subject matter knowledge within the context of lesson study. Evidence is provided and validated, suggesting that representations provide valuable insights into the depth and accuracy of the knowledge prospective teachers bring to instructional settings. It is conjectured that those with weak subject matter knowledge may ask too many open-ended questions, and over rely on their students to "remember." Those growing in their understanding may be reluctant to cede ownership to their students while those with strong understanding include many representations in their lessons. (Contains 1 footnote and 3 tables.) [For complete proceedings, see ED500859.]