Extending counting beyond 10 requires learning the teen number names, which follow a less intuitive pattern in English. Numbers 11–20 each represent a quantity, and their names must be memorized. This extends the counting sequence children began with 1–10.
Use a hundreds chart or number line displayed in the classroom. Count physical objects in groups of ten plus some more. Emphasize the 'ten and some more' structure (e.g., 13 = ten and three more).
You already know how to count to 10 — you can say the numbers in order and match each number to an object. Counting to 20 extends that same idea, but there is one new challenge: the names of the numbers from 11 to 20 do not follow a completely obvious pattern, so you need to learn them.
Here is the key idea: every number from 11 to 20 is really *ten and some more*. The number 13 is ten and three more. The number 17 is ten and seven more. If you have a bag of ten apples and five loose apples beside it, you have 15 apples — one ten and five extra. Thinking about it this way gets you ready for bigger ideas like place value that you will learn later.
The number names themselves can be tricky. "Eleven" and "twelve" do not sound like "ten-and-one" or "ten-and-two" at all — those names come from very old words and just have to be memorized. Starting with "thirteen," you can hear a hint of the structure: "thir-teen" (three-ten), "four-teen," "five-teen," and so on through nineteen. But the order sounds backwards compared to how we say larger numbers (we say "twenty-three" not "three-twenty"), which is one reason children sometimes get confused.
A good way to practice is to use a number line or a row of 20 objects split into a group of 10 and a group of extras. Count the first group: 1, 2, 3 … 10. Then keep going, adding one at a time: 11, 12, 13 … 20. Each time you say a number, point to the matching object. This connects the spoken word to a real quantity and helps you avoid starting over from 1 after you reach 10.