Lesson objective: Apply strategies to mentally create number combinations within 20.
This lesson provides an opportunity for students to apply their knowledge and understanding of mental math strategies to a mathematical situation. Students are asked to find the missing numbers in a Magic Square using their knowledge of known facts and strategies.
Key Concept students will use:
 Knowing some addition and subtraction facts from memory helps us solve new addition and subtraction problems.
Skills students will use:

adding and Subtracting within 100; (Grade 2, Unit 1; 2.NBT.B.5)

decomposing strategies; (Grade 2, Unit 11; 2.NBT.B.7)
 applying properties of operations to solve problems (Grade 1, Unit 15)
Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they draw from their own toolkit for solving problems and utilize strategies that have proven to be efficient for them. In this lesson, it will take the form of children determining what strategy would work best for the given situations. Mathematical Practice 6 (Attend to precision) is also a critical practice within this task as students apply strategies that they have been practicing all year. They are focusing on the precision of communication in speech, as well as written form. They will be explaining, justifying, and supporting their choice of strategies as they discuss their reasoning with peers.
Key vocabulary:
 columns
 diagonal
 efficiently
 fluently
 mental calculation
 rows