2nd-Grade Math Assignment

Focus
This assignment is aligned to a first-grade standard (1.OA.C.6), not a second-grade one. In second grade, students should build on what they learned in first grade to mentally add and subtract fluently within 20. In this assignment, three of the five problems appropriately involve minuends in the teens (for example, 18-3), but two problems only involve subtracting within 10 (again, more closely aligned to 1.OA.C.6). The use of number lines is inappropriate for second grade, and students are not required to use any of the mental strategies outlined in second-grade standard 2.OA.B.2. 

Rigor
Second-grade standard 2.OA.B.2 targets procedural skill and fluency through the focus on using mental strategies to add and subtract fluently. The use of number lines provides a visual representation that builds students’ conceptual understanding of what happens during subtraction and a concrete tool to aid students in calculating the correct answer, neither of which are appropriate when attempting to build students’ fluency in computation. 

Practice Standards
This assignment involves one mathematical practice standard, but it does so in an inappropriate way. Students are given number lines to help them subtract, which is related to Mathematical Practice Standard #5 (“Use appropriate tools strategically”). However, this is an inappropriate use of a tool given that standard 2.OA.B.2 targets procedural skill and fluency; students should be solving the problems using mental strategies, not tools like number lines. Furthermore, some problems can easily be solved without using a number line, which makes the focus of the assignment more about how to use the tool than about building students’ ability to choose the most appropriate tool (if needed) to solve a specific problem.