Illuminations: Lost Buttons
Illuminations (National Council of Teachers of Mathematics)

In this lesson and the following one, students investigate subtraction more directly, beginning with the easier “take away” mode.

Illuminations: Finding Fact Families
Illuminations (National Council of Teachers of Mathematics)

In this lesson, the relationship of subtraction to addition is introduced with a book and with dominoes.

Illuminations: Try for Five
Illuminations (National Council of Teachers of Mathematics)

In this lesson, students explore the many ways to decompose numbers, and they build on their knowledge of addition and subtraction to find missing addends.