I teach this strategy in my second grade classroom. I have the students break the numbers into what is called expanded form like this.

18 + 21 would be rewritten as 10 +8 and 20 + 1 Then the students would add up the tens numbers of 10 + 20=30 Then they would add the ones numbers of 8+1=9 And then they could add 30 +9=39

Although this may seem cumbersome to you it is a helpful strategy for student because they can see all the numbers easily. It shows the place value of the numbers in a way that the traditional way doesn't. It is also a great strategy for advanced students that can start doing these in their heads.

I tell my students and parents that I want to teach many different methods of solving problems so students have an arsenal to use when solving problems. I also teach the traditional borrow and carry method that most parents are familiar with (it is called regrouping now.)

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