Count to 100 by Ones and by Tens

Lesson 1 of 1: Counting and Cardinality

In this lesson:

• Count all the way to 100, one number at a time
• Skip count by tens: 10, 20, 30... all the way to 100
• Find patterns in the counting sequence

Learning Objectives

By the end of this lesson, you should be able to:

1. Count from 1 to 100, one number at a time
2. Count by tens: 10, 20, 30... all the way to 100
3. Find patterns in the counting sequence — teen numbers and decade names
4. Use a hundreds chart to identify and follow counting patterns

How High Can You Count?

You already use counting every day:

• Counting steps as you walk up stairs
• Counting toys before putting them away
• Counting snacks at snack time

How high can you count right now?

Counting 1 to 12

Numbers 1 through 12 each have their own special name:

• 1–5: one, two, three, four, five
• 6–10: six, seven, eight, nine, ten
• 11–12: eleven, twelve — special names to memorize!

The Teen Numbers: 13 to 19

• 13 → "thirteen" (not "threeteen"!)
• 14 → "fourteen"
• 15 → "fifteen" (not "fiveteen"!)
• 16, 17, 18, 19 → sixteen, seventeen, eighteen, nineteen

Counting 1 to 20

Together, 1 through 20 is your most-used range:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20

20 = twenty — our first decade number!

Can you count along without looking?

Quick Check!

What number comes next?

• twelve → ___
• fifteen → ___
• nineteen → ___

Think before the next slide...

Count the Objects

How many stars do you see?

Touch each one and count out loud!

You Know 1–20!

✓ Numbers 1–12: unique names to learn
✓ Teen numbers 13–19: end in "-teen" (with a few surprises!)
✓ 20: our first decade number

Now let's explore 21 to 100!

There's a pattern that makes it much easier...

The Decade Pattern: 21 to 100

Every decade repeats the same structure:

• 20s: 21, 22, 23, 24, 25, 26, 27, 28, 29 → 30
• 30s: 31, 32, 33, 34, 35, 36, 37, 38, 39 → 40
• 40s: 41, 42, 43, 44, 45, 46, 47, 48, 49 → 50

The ones digit counts 1–9, then we jump to the next decade!

The Hundreds Chart

Each row is one decade — ten numbers across

What do you notice about the columns?

Watch Out: Decade Transitions!

The trickiest spots are where decades change:

• 28, 29, 30 (not "twenty-ten"!)
• 38, 39, 40 (not "thirty-ten"!)
• 48, 49, 50 (not "forty-ten"!)

When you hit a nine → jump to the next decade!

Quick Check: What Comes Next?

• 29 → ___
• 49 → ___
• 79 → ___

These are the tricky decade transitions!

Let's Count Together

Follow the hundreds chart — count row by row:

1, 2, 3 ... 10,
11, 12 ... 20,
21 ... 30 ...

Point to each number as you say it!
Go all the way to 100!

Counting by Tens

Instead of counting one by one, we jump by groups of ten:

10 → 20 → 30 → 40 → 50 → 60 → 70 → 80 → 90 → 100

Each jump = one whole group of ten

Counting BY tens: 10, 20, 30... NOT 1, 2, 3...10!

Groups of Ten

One full ten-frame = one group of ten

One ten = 10. Two tens = 20. Three tens = 30.

Tens on the Hundreds Chart

The skip-counting numbers are the last number in each row:

10, 20, 30, 40, 50, 60, 70, 80, 90, 100

These are the "decade numbers" — one per row!

Your Turn: Count by Tens!

Fill in the missing numbers:

10, ___, 30, ___, 50, ___, ___, 80, ___, 100

Say each number out loud as you fill it in!

Key Takeaways

✓ Numbers 1–12 have unique names to memorize
✓ Teen numbers 13–19 end in "-teen" (with a few exceptions!)
✓ From 21–100: each decade counts 1–9, then jumps to the next ten
✓ Counting by tens: 10, 20, 30... each jump is one group of ten

Watch out: After 29 comes 30, not "twenty-ten"
Watch out: "Thirteen" and "fifteen" don't follow the regular pattern
Watch out: Counting BY tens means 10, 20, 30... not 1, 2, 3...10

What's Next?

Next lesson: K.CC.A.2 — Count forward from a given number

You already know the whole sequence 1–100.
Next, you'll practice starting from the middle:

• Start at 7 and count on: 7, 8, 9, 10...
• Start at 47 and count on: 47, 48, 49, 50...

Counting on from any number is a superpower!