Lesson objective: Understand and extend the counting sequence starting at any number less than or equal to 99. In this range, students will be able to read, write, and represent objects with a written numeral.

Students bring prior knowledge of writing and representing objects with a written numeral through 20 from K.CC.3. This prior knowledge is extended through 99 as students begin to understand the patterns within numbers. A conceptual challenge students may encounter is understanding the value of a number in the place value system, believing that the value of ten ones is not equivalent to one group of ten. Building on work from previous units, students use concrete representations to understand the relationship between ten ones and one group of ten. Additionally, students will have difficulty understanding the difference between counting ones versus counting tens, not understanding how each affects the value of a number. This key concept will address this misconception by focusing on the patterns of numbers in the counting sequence.

The concept is developed through work with reading and writing numerals with the use of mathematical tools such as a number path or hundreds chart, which helps students to understand the relationship between numbers in the counting sequence when ten more is counted.

This work helps students deepen their understanding of operations through counting, interpreting values of numbers, and exploring relationships among numbers. Through these activities students will develop a visualization of the base ten number system and the patterns and relationships between numbers.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they will look closely at the relationship between two numbers in the counting sequence through the use of mathematical tools, understanding the value and patterns of numbers in sequence.

**Key vocabulary:**

- count
- digit
- ones
- pattern
- tens
- value

**Special materials needed:**

- hundreds chart