The previous days of this unit have set the stage for this portion of the lesson. Each day has practiced the precursor skills necessary for the subtraction strategy: Down and Under Ten. In Day 4 of this unit, students were exposed to a math talk and purposeful practice that prompted using a number line or ten frames to model this strategy. 

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

• Understanding hierarchical inclusion allows for flexible composing and decomposing of numbers
• Numbers can be decomposed by separating a whole into two or more parts
• Subtraction names the missing part in terms of the whole
• Subtraction can be used in either take away, comparison, or missing addend situations.
• Models can be used to connect concrete to abstract
• Down and Under Ten is a strategy that is dependent on the knowledge of other facts, known as a derived fact strategy

Students might write and/or model their responses 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 Day 4 of this unit, students were exposed to math talks related to specific tools that could be used to model the Down and Under Ten strategy. These number talks will provide more opportunities for students to practice this strategy. The last prompt in the set pushes the strategy beyond the teen numbers to give educators the opportunity to see if the students can extend their understanding.

Prompts:

16 – 7

12 – 8

23 – 7

Show students the following visual math talk prompt and be prepared to pause the video where indicated:

A ten frame is another visual tool that demonstrates the Down and Under Ten strategy. Students can see that when 7 is decomposed into 6, the 6 can be removed from the second ten frame, then just 1 more needs to be removed.

Encourage students to recognize that a ten frame that just has one missing must be 9. Some students may need to recount this amount until they feel comfortable trusting the visual.

Show students the following visual math talk prompt and be prepared to pause the video where indicated:

A number line has been used to consolidate the prompt. If needed, a ten frame can also be used to solidify the thinking.

It is possible that students will count back 4 because of the small “count back”. Encourage students to make the connection to the Down and Under Ten strategy.

4 can be decomposed into 2 to be easily subtracted from 12 to make ten. Then the facts of ten can be used to solve 10-2.

Show students the following visual math talk prompt and be prepared to pause the video where indicated:

This number prompt may be a stretch for some students as it moves beyond the teen numbers. The numbers have been chosen to judge possible next steps of this unit.

Encourage students to use a flexible tool like an open number line to demonstrate their thinking.

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