Your students successfully completed a lab session, correctly filled in all of the worksheets, and collected the required data. Yet, as a science teacher, you still find yourself wondering—what did my students actually learn? And, can they apply that learning to what is going on in their everyday lives? The process of critical thinking and knowledge application requires more than rote memorization and the ability to get answers correct on lab reports or multiple-choice tests. Purposeful, guided reflection may be an opportunity to gain insight into what students are thinking and learning in relation to science content. This article describes how to use guided reflective writing in the science classroom to provide a window into students’ minds.