Students will demonstrate the concepts and skills that they have developed through this context and learning experience.

The purpose of this assessment is for students to demonstrate their understanding of the following big ideas.

• The action of removal is represented by subtraction.
• Removal problems can be solved by addition or subtraction.
• Unitizing 10 single cookies into one group of 10 cookies.
• When adding two digit numbers, regrouping 11-19 single cookies in the partial sum into a group of 10 and some leftover singles.
• Addition and subtraction problems within 100 can be solved using strategies along a developmental continuum of counting all, counting on/back, and using place value strategies. 
• When students are using place value strategies to solve addition and subtraction problems within 100, they are using their understanding of tens and ones and decomposition to accurately, flexibly, and  efficiently solve problems. See the Student Approaches section in this guide for examples.
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The independent assessment will allow students to demonstrate concepts and skills related to the following learning goals:

• I will write an equation that  represents the story situation.
• I will use a model such as a diagram or equations to show how I solved the problem.
• I will accurately solve subtraction problems using appropriate strategies.
• I will write a subtraction story that matches a given equation.
• Students might write and/or model their answers independently. Students can also be interviewed by their teacher.

An alternative assessment opportunity should be offered if this tool will not successfully capture what the student knows, understands or can do.

In order to encourage the place value strategy of keeping the first number (the minuend) whole and subtracting the second number  (the subtrahend) in parts, work through this number string with your class one problem at a time. As you present a problem, provide students with some individual think time to mentally solve it. When students share their response and reasoning, consider modeling their thinking on an open number line in order to make it visible to their classmates.

Note: Watch How to Facilitate the Day 4 Math Talk for a model of what this lesson looks and sounds like.

The first four problems go together. After solving the first three problems, some students might realize they already have the answer when you show 67-39. The three helper problems are helping them to learn how to subtract by parts using place value strategies.

The next four problems go together in another set to support student understanding of place value strategies in subtraction situations. First, some tens are taken away in 73-40. Then, to get us to a landmark (multiple of ten number) some of the ones are taken away in 33-3. Then, the rest of the ones are taken away in 30-5. As with the first set, some students may realize that they already have the answer to the final problem 73-48 when it is presented.

The final two problems, 82-27 and 76-48, are opportunities to practice using place value strategies without the support of helper problems. 

67 – 30

37 – 7

30 – 2

67 – 39

73 – 40

33 – 3

30 – 5

73 – 48

82 – 27

76 – 48

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We suggest collecting this reflection as an additional opportunity to engage in the formative assessment process to inform next steps for individual students as well as how the whole class will proceed.

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