10 More or 10 Less
Mentally find 10 more or 10 less than a given two-digit number without counting
Lesson
Set out your lesson
“10 More or 10 Less means changing a two-digit number by one ten without counting one by one. On a hundred square, ten more is the number straight down one row; ten less is straight up one row. The ones digit stays the same; the tens digit goes up or down by one. We practice a few numbers, then try without pointing at every square.”
Bring to the table
- Paper and pencil (or a printed 1–100 number square if you already have one)
- About 20 large counters or dried beans for the first models only (parent keeps tiny pieces away from mouths)
Extra for the adult
Worked example. Ten more than 24 is 34; ten less than 34 is 24. The ones digit stays the same; only the tens digit changes by one. On a hundred square that looks like a vertical move of one row.
Optional challenge. For 10 More or 10 Less, ask ten more than 89 and ten less than 12, then explain what happens near the edge of the hundred square. Optional: invent one short “ten more / ten less” story using a number from the room (page number, house number digits) without needing a private address.
What to notice. Keep one parent note: starting numbers tried; ten-more and ten-less answers; whether a square or counters were used; support used. A photo of a blank square alone does not show the reasoning. This session samples a few two-digit numbers, not the full 1–100 range.
Share and support
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Teaching approaches
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1 approach
10 More or 10 Less means changing a two-digit number by one ten without counting one by one. On a hundred square, ten more is the number straight down one row; ten less is straight up one row. The ones digit stays the same; the tens digit goes up or down by one. We practice a few numbers, then try without pointing at every square.
Spend about 12 minutes finding 10 more and 10 less for a few two-digit numbers, first with a simple number square sketch or counters in tens, then with spoken answers and a brief check.
Family records and proof options
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Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
Illustrative Mathematics · Practice link — not the full lesson
Number Square
Before you open · source notes
A 1–100 square supports adding or subtracting ten and explaining a vertical move. This is an adult-led sequence, not an independent mastery test.
Free, no sign-in. Use the student view with your child.
Before you openAsk what changes when the learner moves one row down, then try a new number. Repeating the page is not a mastery score.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public Illustrative Mathematics task page. The .html address responds HTTP 308 to this URL. An anonymous GET of this URL on 2026-11-10 returned HTTP 200 with no login or payment prompt. Where a teacher solution is present, it is on the same page as the student task; this check did not find a separate locked student view. An adult can use the student view section and should not read a solution aloud. Advertising was not observed in the fetched HTML text; that is not a browser, device, or ad-free guarantee. This is a paper or discussion task, not an automatically marked interactive game. Opening the link does not save practice or assess mastery. Diagrams on the page use missing or filename-only alt text, so they are not an accessible image equivalent. Accessibility still depends on an adult describing the picture.
Illustrative Mathematics. “Number Square.” Licensed CC BY-NC-SA 4.0. External task; Gakuva does not copy, host, embed, or redistribute it.
CC BY-NC-SA 4.0 — link only
Check understanding
- Given 56, quickly say 66 is 10 more and 46 is 10 less
- Explain that adding 10 increases the tens digit by 1
- Answer '10 more than 73' without using fingers or counting on
“Can your child quickly tell you what is 10 more than 43 or 10 less than 71 — without counting up or down one at a time?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Number Representation & Place Value
- Age range
- Ages 6–8
Standards