Math Quiz

I entered this one in a contest where the subject was "Eraser"

Math Quiz

In arithmetic, he wasn't strong.
This math quiz was taking so long.
It was hard to divide.
Still, he tried till he cried,
but the answers kept coming out wrong.

He would solve and immediately doubt
if he'd taken the most proper route.
He'd retry, but alas,
by the end of the class,
his eraser was simply worn out.

The bell rang. The quiz was now due,
but his sheet was a sad sight to view.
There was nothing but air
in assorted spots where
the eraser wore all the way through.

The tests were collected and sent
to the teacher for grading. She went
through each page in the stack
and then handed them back.
He saw his grade: ninety percent!

He pondered his luck with a frown...
To the head of the class from class clown?
Was he smart? Well not quite,
every one he got right
had shown through from the next paper down!