Two studies were conducted to examine content knowledge changes following 2 weeks of professional development that included scientific research with university scientists. Engaging teachers in scientific research is considered to be an effective way of encouraging knowledge of both inquiry pedagogy and content knowledge. We used concept maps with two cohorts of teachers to assess changes in science teacher knowledge. In study 1, 34 teachers developed pre- and post-concept maps in one of the nine different content areas. A repeated measures analysis of six quantitative scores showed statistically significant increases in knowledge representation. Quantitative and qualitative scoring methods indicate that concept maps are effective for assessing teacher knowledge gains from professional development. Study 2 replicated the results with 24 teachers and provided further information about how knowledge changes.