Unit 9, Lesson 1
Sumas y diferencias hasta 20
Grado 2
Preparation
Lesson Purpose
The purpose of this lesson is for students to fluently add and subtract within 20 using mental strategies.
Lesson Narrative
In this lesson, students find the value of sums and unknown addends from memory in expressions with values within 20. In the first activity, students complete an inventory of sums within 20 and identify those sums that they do not know yet from memory. In the second activity, they continue to practice fluency with addition and subtraction within 20.
Throughout the lesson, encourage students to share the methods they use to recall or find a sum or difference fluently. These include methods based on using the relationship between addition and subtraction, decomposing to get to a ten, and creating expressions that are equivalent, but easier to find mentally.
- Action and Expression
None
- Identify the value of sums and differences within 20 and explain (orally) mental strategies for identifying the value of sums and differences that are not yet known from memory.
- Encontremos mentalmente el valor de algunas sumas y diferencias.
Required Materials
Activity 2
Required Preparation
None
Suggested Centers
NoneTeacher Reflection Questions
Which sums within 20 did students show they are still working on? How can you make time for practice with these sums during the school day?
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