Why ZooDad does not homeschool

Since ZooDad was home doing pre-trip to Maryland stuff, he watched the rest of the inhabitants while I took M to the Evil Public School for the first day of Speech therapy of the new school year. (By the way the 2 PS girls that was supposed to be there, never showed up. Their teacher forgot to send them. How's that for dedication to children with special needs.)

As I left, J started his math. ZooDad helped him.
When I got home 45 minutes later. J was still doing math and looking very frustrated.

Wouldn't you know it, the day I hand over the reigns is the day a totally new concept was introduced.

The instructions read: Write a subtraction sentence to determine the number for n and find that number
The example problem showed that there were 5 girls and some number (n) of boys on the bus. There were 12 children on the bus. How many were boys?

The example showed that you set up the problem like this:
5 + n = 12.
You could then change this to a subtraction sentence (because we have studied fact families) by writing it as 12 - 5= n and then just do the problem.

So what did ZooDad do?
He taught him to solve for an unknown quantity.

Yep. He told him to subtract 5 from each side to isolate the unknown reduce the answer.
The poor, 9-year-old boy was writing out this for each and every answer. 50 in all.
5 + n = 12
5 + n-5= 12-5
0+n=12-5
n=7

But he didn't know why this worked. He was confused and frustrated. ZooDad could explain the process but not the reason why. Or at least not on a 4th grade level.

So when I got home, I spent about 15 minutes with our balance, and unifex cubes showing how equations had to be equal and that as long as you added or took away an equal amount from both sides, the equation would stay balanced. We practiced finding out the unknown quantity in the balance bucket by comparing it to a known number on the other side and then subtracting them until it balanced.

Then I showed him the shortcut of just converting it to a subtraction sentence. (Which is what the book asked him to do in the first place.)

ZooDad said he thought that it seemed a bit difficult for 4th grade math.