A/N, hello again my next theory is that Snape is James Potter in disguise. One Shot will be with sequels.
Snape sat down with a grunt. He had to grade yet more of those stupid essays. He wondered how they could turn them in looking like they did, like his enemies had looked after he and his friends had hexed it six different ways into a rag-like mess. He looked back at the essays piled on his desk, and spotted the one he was after. His son's essay, he grabbed it, feeling its steady weight on his hands. They were his hands at the moment, as this was his body. He had cast a shielding spell on the door, a very powerful one, keyed only to him, and his other self. He actually read the essay, as he had with none of the others and sighed slightly. Harry had definitely inherited his mother's potions ability. He itched, straining to give the essay the O it so very much deserved, but realising he had to keep in character, marked it with a D for Dreadful.
The next morning, Harry was shocked to discover that he had actually got a D in potions. The highest grade he had ever received. Chancing a glance at Snape, he started as the professor made eye contact and, quite definitively winked.
A/N next story, Finding out.