Standard Description of 6.EE.A.4: Identify when two expressions are equivalent (i.e., when the two expressions name the same number regardless of which value is substituted into them). For example, the expressions y + y + y and 3y are equivalent because they name the same number regardless of which number y stands for.
Standards preceding 6.EE.A.4 are 5.OA.A.2. Standards that are taught after students master 6.EE.A.4 are 7.EE.A.1. The Lumos Coherence map for 6.EE.A.4 includes standards correlations, description and a list of apps, questions, videos, books and other resources related to 6.EE.A.4