A Complex Argument

What To Look For In This Video

This 3rd Grader has had lots of experience with word problems. She already understands what it means to "take away" 25 from 63.
And she already understands that she can think of 2-digit numbers in terms of tens and ones. In particular, she thinks of 25 as 2 tens and 5 ones and 63 as 6 tens and 3 ones.
She took the 2 tens of the subtrahend from the 6 of the minuend - without saying that that is what she was doing.
She then broke up an additional ten of the minuend. She recorded "30" to represent the 3 tens that she had left.
In order to now take 5 ones, she took the 3 ones of the minuend and then 2 additional ones from the ten that she had broken up.
That left her with 8 ones - which she recorded.
She is able to explain her work - in effect proving that her answer is correct.