Although assessment of student progress in word reading skills is common, students' knowledge and skills for comprehending informational text are rarely assessed. Despite research indicating the need for instruction in this area and a growing national understanding of its importance that is reflected in the Common Core State Standards, few formative assessment tools are readily available and used to assess informational text comprehension. In this study, teachers who were randomly assigned to an experimental group were provided with ongoing professional development on how to administer and interpret the newly developed Concepts of Comprehension Assessment in their classrooms. The assessment was designed to help assess and consequently encourage instructional attention to students' skills for comprehending informational text. Those students in the experimental group showed greater growth on the Concepts of Comprehension Assessment and on a writing task.