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Level 1Grade 1skill: order_to_20· 7 min read

Ordering Numbers to 20

In short: Ordering numbers to 20 is just count order. To sort smallest-to-greatest, keep picking the smallest number left until the pile is empty. "Just before" means one less, "just after" means one more, and a number with a ten always beats a single digit.

How to order numbers up to 20

Ordering numbers just means lining them up in count order — the same order you would say them if you counted from 1. If someone asks for smallest to greatest, you want the numbers in the order you reach them while counting up. Greatest to smallest is the same line walked backwards.

Here is the one trick that makes all of it easy: don't try to compare every number at once. Find the smallest, set it down, then find the smallest of what is left. Repeat until the pile is empty. Ordering is really just find the smallest done over and over.

A number line taped to your desk, or drawn 1 to 20, never lies. Whichever number sits further to the left is smaller, because you would count to it first.

  1. Read the question and circle the direction: smallest-to-greatest or greatest-to-smallest.
  2. Count up from 1 in your head (or use a number line) to find the smallest number in the list.
  3. Write that number down first, then cross it off the list.
  4. Find the smallest of the numbers that are left, and write it next.
  5. Keep going until every number is placed.
  6. If the question asked greatest-to-smallest, flip your finished line around.

Why counting order is the whole secret Why it works

Count-up rule
The number you say first when counting up from 1 is the smaller one.

Counting up you reach 11 before 17, so 11 is the smaller number.

Tens first
A number with a ten is bigger than a number with no ten; that is why teen numbers beat single digits.

19 is bigger than 9 because 19 has a ten in it and 9 does not.

Neighbours
Just before a number is one less; just after is one more.

Just before 14 is 13, and just after 14 is 15.

Notice that lining numbers up, filling a gap, and naming a neighbour are not three separate skills but one: each simply asks where a number sits on the count from 1 to 20. Get that sequence automatic and every version of the question answers itself.

Worked examples

Put these in order from smallest to greatest: 14, 8, 11. = 8, 11, 14
  1. The smallest of the three is 8, so write it first.
  2. Of the two left (14 and 11), 11 is smaller, so it comes next.
  3. Only 14 is left, and it goes last.
What comes just before 16, just after 16, and between 12 and 14? = Before 16 is 15, after 16 is 17, and between 12 and 14 is 13.
  1. Just before 16 means one less: 16 − 1 = 15.
  2. Just after 16 means one more: 16 + 1 = 17.
  3. Between 12 and 14, count 12, 13, 14 — the middle number is 13.
Fill the gap: 15, 16, ___, 18. = 17
  1. The numbers climb by one each step.
  2. After 16 the next count is 17.
  3. Check it: 15, 16, 17, 18 — smooth, so the blank is 17.
Order from smallest to greatest: 17, 7, 20, 11. = 7, 11, 17, 20
  1. 7 and 17 sound alike, but 17 has a ten, so 7 is the smallest — write it first.
  2. The next smallest is 11.
  3. Then 17, and last of all 20.
Order from greatest to smallest: 9, 19, 13. = 19, 13, 9
  1. Greatest first this time. 19 has the most, so it leads.
  2. The next biggest is 13.
  3. Smallest is 9, so it goes last.

Common mistakes

Landing one number off

✗ 17

Asked for the number just before 16, this student counted the wrong way and landed on 16's other neighbour, 17. "Just before" always means the number you say one step earlier when counting up, not one step later.

Fix: Point at the number on a number line and take exactly one step left for "before" (one less) and one step right for "after" (one more). Just before 16 is 16 − 1 = 15.

off_by_one

Ordering the wrong direction

✗ 15, 12, 9

Asked for 9, 15, 12 from smallest to greatest, this student lined them up greatest-to-smallest instead. The values are right, but the whole line runs backwards.

Fix: Circle the direction words before you start. Smallest to greatest means the tiny number leads: 9, then 12, then 15. If your first number is the biggest one, flip the line around.

reversed_operands

Practice: Ordering numbers to 20

Line them up, name the neighbour, and fill the gaps. Count from 1 whenever you are unsure, and always check the direction the question asks for.

Keep going

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Frequently asked questions

What does "just before" and "just after" mean?

Just before a number means one less than it, and just after means one more. Just before 14 is 13; just after 14 is 15. On a number line, "before" is one step left and "after" is one step right.

My child mixes up numbers like 7 and 17. How do I help?

They sound alike, but 17 has a ten inside it and 7 does not, so 17 is always bigger. Building both with counters — seven singles versus a ten-stack plus seven — makes the difference something they can see and hold.

What is the difference between smallest-to-greatest and greatest-to-smallest?

They are the same set of numbers, just faced opposite ways. Smallest-to-greatest starts with the tiny number and climbs; greatest-to-smallest starts with the biggest and comes down. Always read which direction the question asks for before you write.

Do you have to count from 1 every time?

Not forever. Counting up from 1 is the reliable check when a number is tricky, but with practice most children start to just know that 12 comes before 15. Keep the count as a safety net for the hard ones.

Why do teen numbers confuse young children?

The names are sneaky: "eleven" and "twelve" give no hint of the ten, and "thirteen" says the ones part (three) before the ten. Focusing on the count order, and on the fact that every teen number has one ten, clears most of the confusion.