youcubed: Estimating Dots (K)
youcubed (Stanford University)

This activity is a valuable opportunity for students to think about estimation and making visual justifications related to the approximate number system.

youcubed: Flexible Number Trains (1-2)
youcubed (Stanford University)

In this activity we focus on numbers that can be created by repeated addition, summing the same number again and again to achieve the result.

Illuminations: Focus on Two
Illuminations (National Council of Teachers of Mathematics)

A nursery rhyme provides a context for using the number 2.