Writing in science is a natural way to integrate science and literacy and meet the goals set by the "Next Generation Science Standards" ("NGSS") and the "Common Core State Standards" ("CCSS"), which call for learners to be engaged with the language of science. This means that students should record observations, thoughts, and data as scientists do, but more important, they should engage in the practices of making and defending claims, engaging in argument based on evidence, and communicating what they have learned. Science notebooks are one means to engage students with the scientific practices and the language of science. Notebooks serve as a means to record observations, collect data, and summarize investigations; however, they should also be used to explain thinking, to develop arguments that demonstrate understanding, and to connect ideas across concepts. These latter tasks are associated with higher student learning. This is what the K-5 teachers the author worked with came to realize as they analyzed their students' notebooks within a professional study group, with some participating over a four-year period. The teachers met once a month to discuss science notebooks and professional literature related to writing in science in order to improve their practice. This article highlights the teachers' progress over time as they moved from mechanical to insightful use of science notebooks.