A conclusion with the topic of social inequality can run in a variety of ways and I think that much of it is dependent on what you have composed in the body of the essay.  Without knowing this, I think that you might have to bear the brunt of determining how a great writing sample must be concluded.  I could suggest some ideas, though.  I think that composing a conclusion that argues that social inequalities could represent Wilson's symbol of "fences."  Social inequities "keep out" individuals from achieving their dreams, and their hopes.  We see this with Troy and the frustration he experiences on both racial and class levels.  This could be something in the conclusion that is applied to other characters' experiences.  Another potential closing point could be to analyze where Wilson stands on the issue of race or class constitituing a larger social inequality.  Seeing that both operate in an almost tandem like quality in the play, is there one that might weigh heavier than the other?  Using the conclusion to explore this topic could be quite thought provoking.

The conclusion should recapitulate the main thesis. If you have a strong thesis and strong arguments that support your thesis, then the conclusion should show how it all fits together. You could even say something, like:

In light of the discussion, the conclusion that social inequalities should be clear for these reasons...

One mistake that I see once in a while in a conclusion is that people add something new. This is almost never a good idea, because it leaves the reader with something other than your thesis in view at the end. So, summarize.