Adding two numbers with a sum to 20 extends earlier skills using strategies like counting on, making ten, and ten-frame visualization. Fluency with these facts is fundamental to later arithmetic.
Use ten frames, number lines, and manipulatives. Emphasize the commutative property. Practice counting on rather than recounting from one.
You already know how to add numbers within 10. Adding within 20 extends that skill to slightly larger sums — like 8 + 7 or 9 + 5 — where the answer crosses above 10 into the teens. The key is having good strategies, not just counting every object from the beginning.
The first strategy to practice is *counting on*. Instead of starting at 1 and counting all the way up, you start at one of the numbers and count on from there. For 8 + 6, you hold 8 in your head and count on six more: 9, 10, 11, 12, 13, 14. This is much faster than counting from 1. And because addition does not depend on order (7 + 9 is the same as 9 + 7), you can always start with the *bigger* number to make the counting even shorter.
The second and more powerful strategy is *making ten*. The number 10 is special: it is easy to work with because of how our number system is organized. When you see 8 + 6, you can notice that 8 is only 2 away from 10. Split the 6 into 2 and 4, use the 2 to get from 8 to 10, then add 4 more to get 14. This takes practice to do fluidly, but once it clicks it works for almost every sum in this range. A ten-frame — a grid with two rows of five boxes — is a great tool for visualizing this strategy.
Teen numbers (11 through 19) sometimes feel tricky because their names in English do not obviously show their structure. But every teen number is just ten plus some more: 13 is ten and three, 16 is ten and six. When you make ten as part of your strategy, the answer always comes out clearly as a teen number. Recognizing teen numbers as "ten plus something" connects addition within 20 to your understanding of place value.
With enough practice, many of these facts will become automatic — you will just know that 7 + 8 = 15 without counting at all. That fluency matters because it frees up your attention for harder problems later. But the strategies (counting on, making ten) are not just crutches for beginners: they are genuinely good mathematical thinking, and understanding *why* 7 + 8 = 15 is more valuable than simply memorizing it.