You may have seen this purported parent response to a homework question on Facebook or even the Colbert Report.
I thought it was time to help Jack and explain what the teacher was probably thinking when he or she assigned this problem.
You did a great job using the number line to figure out this subtraction problem. It looks to me like you forgot about the tens jump. Remember 316 means 3 hundreds, 1 ten, and 6 ones. I see you took away 3 hundreds jumps and 6 jumps of one, but missed the 1 jump of ten.
I hope this helps.
A Math Teacher
Another aspect of the Common Core this teacher was working towards was Mathematical Practice 4: Construct viable arguments and critique the reasoning of others. Whether or not you agree with Jack’s method, being able look at someone else’s work, figure it out, and help them fix the errors, is an important skill.
While many of us are not familiar with the particular models that are being used to develop students’ conceptual understanding, those of us who have seen the shift in student comprehension of mathematics agree that these models can serve as a very important bridge between just “doing” math and actually understanding it.
By Jim Town – Mathematics Specialist at ACOE Core Learning