TEACHER EDITION

Counting by Tens or Ones

Grade 2 · Lesson 2 · Dimensions 2A p.8
Math Book 2 · sheet 2
Warm-up — yesterday: Tens and Ones
How many tens and ones in 58?
5 tens 8 ones

What we are learning

Counting on by ten changes only the tens digit. Counting on by one changes only the ones — until the ones run out.

How it is done — keep this beside you

These steps stay on your page while you work. If you get stuck, find the step you are on and read it again before you put your hand up.

1
Start at 34.
34
2
Add one ten. Only the tens digit moves.
34 34 → 44
3
Another ten.
34 34 → 44 34 → 44 → 54
4
Now back to 34 and add ONE. Only the ones digit moves.
34 34 → 44 34 → 44 → 54 34 → 35
5
Ten changes the tens. One changes the ones.
34 34 → 44 34 → 44 → 54 34 → 35 +10: 34→44 +1: 34→35

Practice

I DOteacher builds it, nothing erased
Count on by tens from 26, three times.
  1. 26 + 10 = 36
  2. 36 + 10 = 46
  3. 46 + 10 = 56
  4. 26, 36, 46, 56
WE DO 1together, on whiteboards
Count on by tens from 41, three times.
Only one digit should be changing. Boards up after each step.
  1. 41, 51, 61, 71
WE DO 2together, on whiteboards
Count on by ones from 67, four times.
Careful at the end of this one.
  1. 67, 68, 69, 70, 71
YOU DOindependent, from the book
Book 2A p.8 — the Do section, clipped onto the slide
the book page
Ask yourself: “Which digit should be changing?”
Watch for
The second WE DO crosses 69→70 deliberately. That crossing is where counting by ones stops being automatic, and a child who writes 610 has shown you exactly what they think a number is.