In the play The Glass Menagerie, are the characters failures just because they didn't reach their goals?
Your question presumes that each of the characters had a goal and that they either clearly did or did not reach those goals. Let's see if that's true:
Amanda's goal for Laura seems to be to help her be self-sufficient, either through a career or through marriage. In the end she has neither a career nor a husband. Is that failure?
Amanda's goal for Tom is less clear, as she relies heavily on him to achieve the goal for Laura. What is the goal?
Amanda's goal for herself is buried in her ambitions for her children. Does she succeed?
Tom's goal is clear from the start--to leave his miserable life and be free. He succeeds at half the goal; does he succeed at the other?
Laura's goal seems to be to avoid most human contact, which she does until Jim arrives. What happens after their "date" is not as clear.
Jim's goal is more like his ambition--to be more than just a shoe warehouse foreman. Does he make something of himself?
Think about those questions, and once you have the answers from your own observations and perhaps some class discussion you'll be able to write your essay.