(Numbers and Operations > Operations with Rationals > Addition and Subtraction > Integers)
The interactive number line tool in Adding a Negative and a Positive Integer Using a Number Line is ideal for students’ first experience with adding integers of different signs. As students drag an arrow from an initial location to the final sum, they learn to associate adding a positive value with movement to the right and adding a negative value with movement to the left.
Teachers can use the first few pages of the document as an instructional tool, discussing with students how to use the number line to find the sum.
After a few examples, ask students to predict whether the sum will be positive or negative. Encourage students to share their reasoning with the class. Then test predictions by having a classmate perform the steps on the computer or interactive board as classmates help direct him/her.
A nice follow-up assessment can include students journaling about the process of using a number line to add different signed integers. Challenge students to construct two of their own number sentences, one with a positive sum and one with a negative sum. And just for fun, how about a sum of zero?