What do you mean "what does this mean"? 

So you give me a "B" 

I change my style, I change my content

But my grade remains constant 

I ask you a question on my essay

"Only you know the answer", you say 

We write essays on Thoreau and Emerson

whom you shower with praise

yet their essays are confusing and vague 

so why can't ours be the same? 

You beat the creative out of us like a rag against the wall

No imagery or sensory detail at all

Then expect us to be creative

for our personal narrative 

If our essays should make sense

Then your advice shouldn't be evasive and full of pretense