Understanding Teen Numbers

Introduction

Understanding teen numbers is a foundational math skill that sets the stage for mastering place value and more complex arithmetic concepts. This lesson plan will guide your learner through the journey of exploring teen numbers, starting with the concept of individual ones and progressing to understanding the structure of "ten and some ones."

Before beginning the lesson, your learner should be comfortable with number lines up to 10. They should also understand the concept of one more and one less.

Key Concepts for Understanding Teen Numbers

Here are a few concepts that are important to know for the lesson:

• Teen Numbers as Individual Ones: Learners begin by thinking of each teen number as a collection of individual ones. For example, they consider 13 as "13 ones." This approach helps learners initially grasp the quantity but does not highlight the inherent structure of the number.
• Teen Numbers as Ten and Some Ones: As learners progress, they are introduced to the concept that teen numbers are composed of a group of ten and some additional ones. This "ten and a bit" structure is crucial for understanding the foundation of place value in the number system.
• Groups of Tens and Ones: Understanding teen numbers as a groups of tens and ones introduces learners to the concept of place value.The first digit in a teen number represents the number of tens, and the second digit represents the number of ones.For example, in the number 14, the digit "1" represents one group of ten, and the digit "4" represents four additional ones.
• Dual Counting: Dual counting involves counting teen numbers in two different ways to reinforce their structure, usually the traditional way of counting and an alternative way based on the "tens and ones" structure. Traditional counting: “eleven, twelve, thirteen…” Alternative counting: “one-ten one, one-ten two, one-ten three…”
• Names of Teen Numbers: Teen number names can be confusing because they do not follow a consistent pattern and do not always reflect their numerical structure. Numbers like "eleven" and "twelve" lack the "teen" suffix. "Thirteen" and "fifteen" also present difficulties due to irregular spellings.

Teaching Plan

The following activities will help your learner become confident with the structure of numbers 11 to 19. Remember to go at a pace that is comfortable for your learner.

Examples and visuals to support the lesson:

1. Introduction to Teen Numbers

• Begin with having your learner think of teen numbers as individual ones. For example, consider 13 as "13 ones."
• Count sets of 11-19 items. Encourage your learner to draw a circle around each group of ten. This helps expose the "ten and a bit" nature of these numbers.
• Explain that the names of these numbers in English do not highlight this structure, unlike other languages (e.g., Chinese and Welsh).
• Use the following sentence stem for description: “There is one ten and ___ ones.”
• Show collections of objects with ten already circled. Demonstrate counting on from ten to find the total number of items.
• Gradually include examples where the group of ten cannot be seen individually as ten ones.

Skill Check
I know that making a group of ten can help me count sets of things.

2. Recording Groups of Tens and Ones

• Introduce recording the quantities using symbols, relating the digits to the structure of the numbers.
• Use a place-value chart to note how many groups of ten and how many ones are in each picture.
• Revisit previous pictures to help your learner relate the concepts more easily.
• Encourage describing the structure of the numbers in full sentences using the stem: “The 1 means one ten and the ___ means one(s).”

Skill Check
I know that the teen numbers are made of one ten and some ones.

3. Exploring Number Names

• Once your learner is confident with the "ten and a bit" structure, explore how these numbers are named.
• Use a representation from a previous example (e.g., 14 pencils) to explain how we articulate the ones first and the tens second (e.g., "fourteen").
• Compare this to other two-digit numbers (e.g., "fifty-four") if your learner is already familiar with them.
• Highlight the different parts of the number names: the "four" relates to four ones, and the "teen" relates to one ten.
• Introduce the idea that if we followed the naming rules for other two-digit numbers, we would call fourteen "one ten four."

Explore the names of all the teen numbers and how they relate to the structure of the number:

• “Fourteen,” “sixteen,” “seventeen,” “eighteen,” and “nineteen” clearly show the ones.
• “Thirteen” and “fifteen” have irregular spellings.
• “Eleven” and “twelve” lack the “teen” suffix, requiring special attention.

Skill Check
I know the names of numbers 11 to 19.

4. Dual Counting Method

• Use dual counting to reinforce the "ten and a bit" structure: Count as “eleven, twelve, thirteen…” and alternatively as “one ten one, one ten two, one ten three…”
• This alternative counting may flow more easily and link closely with “twenty-one, twenty-two, twenty-three…”
• Practice dual counting between ten and twenty. Continue to higher numbers if your learner has already been introduced to them.
• Tap the numbers on a number line, Gattegno chart, or hundred square while counting to embed the link between the name and the digits.
• Periodically stop counting to ask your learner to identify one more and one less.
• Provide missing number problems for practice in identifying missing numbers in the counting sequence.

Skill Check
I can count the teen numbers in the correct order.

5. Estimating Positions on a Number Line

• Work on estimating the position of teen numbers relative to 10 and 20 on a blank number line.
• Initially align a 0-10 number line above a 10-20 number line for your learner to see the relationships between the numbers.
• Gradually move to estimation without the 0-10 number line. Encourage proportional thinking by estimating based on the distances between the numbers.
• Model the thinking process: “Eighteen is closer to twenty than ten, so it sits about here…”
• Provide your learner with a variety of tasks to demonstrate their understanding. For example, ask your learner to place a given number onto the number line. Then point to a spot on the number line and ask them to estimate the number at that position.

Skill Check
I can estimate where teen numbers are on a number line.

Summary

By the end of this lesson plan, your learner will have a comprehensive understanding of teen numbers. They will know the "tens and ones" structure of teen names, grasp the concept of place value, and apply dual counting techniques. Additionally, they will recognize the irregularities in the naming of teen numbers and understand how these names relate to their numerical structure. Equipped with these skills, your learner will be well-prepared to tackle more advanced math concepts with confidence and clarity.

Teaching Plan adapted from NCETM under OGL license v3.