We use data from a teaching experiment with a group of eight years old students to explore the potential of examining number sentences to promote relational thinking. This type of thinking requires attention to mathematical structure through consideration of relationships between terms contained in the sentence and not just on computation and comparison of the numeric values of each side. We show that children came to “know-to act” in the context of written activities and orchestrated discussions about number sentences, overcoming some of their computational habits and developing new ways to see and more flexibly approach the sentences. The results help to advance the study of young students´ emergent algebraic modes of thinking.