Learn how to add two-digit numbers in this Year 2 article from BBC Bitesize. ... When you are solving an addition calculation with a two-digit number, you need to think about tens and ones.

If the two numbers in a place value column add up to ten or more, you must regroup. This means breaking a number up into tens and ones, or hundreds and tens to help with the addition. Let's look ...

The Common Core State Standards teach students the algorithm for multi-digit addition and subtraction in 4th grade. But some experts say it should be taught sooner.