Drawing from a large efficacy study in upper elementary science, this report had three purposes: First to examine the quality of teachers' content-pedagogical knowledge in upper elementary science; second, to analyze the relationship between teacher knowledge and their assessment practice; and third, to study the relationship between teacher knowledge, assessment practice, and student learning. Based on data from 39 teachers, we found that students whose teachers frequently analyzed and provided feedback on student work had higher achievement than students whose teachers spent less time on such activities. Our findings support other research indicating the power of well implemented formative assessment to improve learning. Teacher Content Survey is appended. (Contains 13 tables and 1 figure.)