Your teacher's an idiot. How does one miss all that writing?

I would request the teacher reread your paper and grade it appropriately...

You didn't even print it out? I thought kids today emailed their essays! That's on the teacher, but to be honest I wouldn't have think to check the back of the page either!

Always avoid doing double sided.

Why would you hide text on the back of a page? Are you one of them crazy tree-huggers that thinks they're saving the world by printing on both sides of the page and using semi-colons instead of wasteful full colons?

What exactly were the instructions for this paper? Every paper I ever wrote usually involved the teacher specifically telling us not to print text front and back. I had a teacher once who deliberately only read the front side of the pages for someone's paper because there wasn't supposed to be a back side per the instructions and so they just treated the back as if it didn't exist.

How couldn’t he tell when a sentence that began on the bottom of one page didn’t me sense with the top of the next page? And why wouldn’t he reread and regrade it after he realized his mistake?

I'm giving your teacher a D too - for 'Dunce'. And I have the authority, as both someone with the common sense to check both sides of a piece of paper, and as the Highlander.

Then you need to have your instructor re-grade it due to the fact that your instructor was the one that screwed up. If they refuse, go to whoever is at the next level. You should easily be able to have that regraded.