Middle school mathematics teacher quality is questionable because the number of certified mathematics teachers considered highly qualified is low (Birman et al., 2009). The author examined Grade 8 data from the 2005 National Association of Educational Progress mathematics assessment. The purposes of the study were to (a) determine the impact of middle school mathematics teachers' content knowledge and teachers' mathematics pedagogical knowledge on student achievement and (b) compare the effect of the degree to which teachers received reform-oriented professional development activities on student achievement. The results indicated that mathematics content knowledge has a larger role in predicting student achievement than mathematics pedagogical knowledge. Also, teachers who reported participating in fewer professional development activities had students with higher scores than those students whose teachers reported either participating in more professional development. Results for various professional development activities are also presented.