standard_description: Derive using similarity the fact that the length of the arc intercepted by an angle is proportional to the radius, and define the radian measure of the angle as the constant of proportionality; derive the formula for the area of a sector.
problem_activity: Narrative
The purpose of this activity is for students to choose from activities that focus on counting up to 20 objects or adding and subtracting within 10. Students choose from the centers introduced in previous lessons as well as one introduced in the previous activity. If more than one stage of a center has been introduced, students choose from any of the stages. Students are encouraged to choose the center that will be most helpful for them at this time.
Counting Collections
Number Race
Check it Off
Five in a Row: Addition and Subtraction
Required Materials
Materials to Gather
Materials from previous centers
Required Preparation
Gather materials from:
Counting Collections, Stage 1
Number Race, Stage 3
Check it Off, Stage 1
Five in a Row: Addition and Subtraction, Stages 1 and 2
Launch
Groups of 2
“Now you are going to choose from centers we have already learned.”
Display the center choices in the student book.
“Think about what you would like to do first.”
30 seconds: quiet think time
Activity
Invite students to work at the center of their choice.
8 minutes: center work time
“Choose what you would like to do next.”
8 minutes: center work time
Student Facing
Choose a center.
Counting Collections
Number Race
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Check it Off
Five in a Row: Addition and Subtraction
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Activity Synthesis
“What was your favorite part of center time today? Why was it your favorite?”


aligns: no