Lesson objective: Understand and extend the counting sequence starting at any number less than or equal to 99.

Students bring prior knowledge of counting, writing numbers, 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 bridging counting across decade numbers. For example, counting from 29 to 30 is a difficult transition and students often follow twenty-nine with twenty-ten, because they are following the sequence of counting from 1 to 10.

The concept is developed through work with reading and writing numerals with the use of mathematical tools such as a number path and a 99 chart, which helps students to understand the relationship between numbers in the counting sequence. Students will practice finding a missing value by using the counting on strategy.

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 tse 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

**Special materials needed:**

- counters
- dry erase markers
- whiteboards