Illuminations: Numbers Many Ways
Illuminations (National Council of Teachers of Mathematics)

Students work with subtraction at the intuitive level as they explore number families and ways to decompose numbers to 10.

Illuminations: Fact Family Fun
Illuminations (National Council of Teachers of Mathematics)

In this lesson, the relation of addition to subtraction is explored with fish-shaped crackers.

Illuminations: Who's in the Fact Family?
Illuminations (National Council of Teachers of Mathematics)

In this lesson, the exploration of the relation of addition to subtraction is continued as the students use problem-solving skills to find fact families, including those in which one addend is zero or in which the addends are alike.