Base 10 Lesson 3: Teaching 2-digit addition and subtraction by demonstrating and explaining.

Practice problems:

1. What are the two main goals for teaching 2-digit addition and subtraction (or almost anything else in math)

• Children should know how to do the process (adding or subtracting or whatever)
• Children should understand why the process makes sense and gives you the right answer.

2. How should a lesson be structured so that the teacher demonstration is effective?

The teacher should show how to do [whatever it is] in a way that is as clear as possible

Then the class should repeat the process with the teacher questioning the children, so that the children do as much of the problem as possible.

Often the class will do the process another time, with the children doing all or almost all of the work.

Finally, children do the work independently, and the teacher circulates, observes and helps individual children.

3. What are some advantages of using base 10 manipulatives to teach 2-digit addition and subtraction?

• Using manipulatives is more concrete than using just numbers
• Manipulatives hold part of the information of the problem, which frees up working memory space to focus on the key steps of the process
• Base 10 materials show the relationships between tens and ones, which makes the trading/renaming steps more concrete.

3. What is the key point in using manipulatives to teach 2-digit addition and subtraction?

The transition from using manipulatives to the pencil and paper algorithm. It's important to manage this transition in such a way that the children understand how the two processes are the same.

4. Put these lessons in order:

b. adding using just manipulatives, without exchanging

c. adding using just manipulatives with exchanging

a. adding using both manipulatives and pencil and paper

d. adding using only pencil and paper