Here is a sample lesson from Japan Math Corp's Primary Math International Lesson Book for G1. Students are given space to write their math sentence and also show their work in the "My Idea" section. The illustration does not show the correct number of cards. Students cannot rely on the illustration to help them solve the problem. They cannot merely count the cards in the picture. This student has written out the math sentence and taken out 9 math blocks from their Student Math Block Kit to begin calculating.

Two different students expressing their ideas in two different ways:

This student shares their idea with the entire class using the magnetic Teacher's Block Set.

Their strategy was to add 1 to 9 and make 10 proceeding to then add the remaining 3 left over from the 4. Another student used two sets of blocks and subtracted 1 from the 10 to make the 9 and then added 4 from the second set of blocks. The teacher acknowledges that both ideas are correct and then leads students to discuss which ideas can lead to the correct answer fastest. Here, students will recall the composition and decomposition of numbers up to 10 and "10 and how many" that they learned in Kindergarten. As a result, they will realize that the most sophisticated method is to decompose 4 into 1 and 3 to "make 10."

This unit aligns with the Common Core State Standard of Operations and Algebraic Thinking.

#### Represent and solve problems involving addition and subtraction.

*CCSS.MATH.CONTENT.1.OA.A.1*

*Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.*

#### Understand and apply properties of operations and the relationship between addition and subtraction.