Lesson objective: Understand that objects can be sorted and counted to identify how many are in a category.

Students bring prior knowledge of rote counting and understanding amount counted from Kindergarten, Unit 1.

This prior knowledge is extended to sorting as students sort to identify a category. A conceptual challenge students may encounter is the lack of one to one correspondence.

The concept is developed through work with familiar objects and shapes, which move students from the familiar to the conceptual understanding.

This work helps students deepen their understanding of number because the understanding of one to one correspondence is evidenced through the sorting of objects into categories and answering how many.

Students engage in Mathematical Practice 3 (Construct viable arguments and critique the reasoning of others) as they explain and defend their grouping and sorting choices. Situations offer multiple correct grouping solutions, however the answer to "how many" always remains constant and measurable to the teacher.

**Key vocabulary:**

- category
- group
- identify
- sort

**Special materials needed:**