Description: Explanations and examples of how to implement the Operations & Algebraic Thinking standards in Grade 1. The last cluster in the OA domain deals with understanding the meaning of the equal sign and determining the unknown in an equation. These standards are integral to helping students engage with the 12 different subtypes (see the table above) of addition and subtraction problems. The standards call out the importance of understanding the meaning of the equal sign.*Teacher Advisor is 100% free.