Originally Posted by Irena
Okay so this was an assessment question not a homework question. And my problem is not the question per se but that my DS was marked wrong for it b/c apparently his answer didn't fit the specific formula.

Here it is: "Write a comparing story. Draw a model that matches the story. Write a number sentence that solves the story."

DS wrote as an answer: "There are 70 lego pieces in a lego set. A set of legos containing 80 pieces comes in the mail. How many more legos are in the new set? 70+10=80 "

It was marked wrong and she was wrote in red "'comparing' means subtraction sentence. Or at least explain that the missing part is 10." Then she told me on the phone that DS didn't understand the the difference between the two sets is 10.

Now I am not confident at all in MY math abilities. Seriously. Even at this level LOL. But it seems to me that he not only did what the question asked but he also understood quite clearly the difference in the amounts between the two sets is 10, No? Am I missing something?

He said 70+10=80, so obviously he knows that 80-70=10. If the teacher really, truly believes that your DS "didn't understand the the difference between the two sets is 10" then basically she's hallucinating.

This is a case where "show your work" has become an extremely pedantic ritual with an educational value that is significantly less than zero.