Many children struggle to communicate explicitly about the relationships between variables and concepts that are central to science content. In order for students to talk and write like scientists, they need to acquire ways of using language common in science discourse. For example, in the writing above, the student uses the word "play" in much the same way that the word might be used in everyday discourse. This everyday use of the word contributes to ambiguity in the students' scientific writing. The meaning for the word "play" in everyday use is quite different from the meaning of this word in the context of a statement about the role a variable plays in changing the rate of a process in science. In order to use language effectively in science, students need to add such scientific meanings to their communicative repertoires. As the writing sample above shows, students not only need technical vocabulary but also sentence-level language patterns, or grammatical resources, that facilitate communication of relationships between ideas. In this article, the author's describe an instructional routine called "Explicitly Speaking" that they have used to scaffold this grammatical aspect of students' science language development. The routine is embedded within inquiry-based science learning and draws on key principles of second language acquisition. Just as inquiry-based science instruction can be used across grade levels, the Explicitly Speaking routine can also be used across grade levels. In addition, just as inquiry-based science instruction can be differentiated to accommodate the needs of learners at different levels of science understanding, the Explicitly Speaking routine can be differentiated to accommodate the needs of learners at different levels of language proficiency. Strategies for this differentiation are discussed in this article.