Are you referring to The Lesson by Toni Cade Bambara? If so, you can read an excellent analysis of the story and the others in the collection right here on enotes.
Two major assumptions are that all the children are poor and that they are minorities.
In this story, "the lesson" is different for each of the children involved. Sugar gets one thing out of the field trip to the expensive toy store, F.A.O. Schwarz, and Sylvia gets something entirely different out of it. Since all of the children that live in the apartment complex are poor, their poverty affects how they view life. Nevertheless, they are all individuals and their individuality also affects how they view life, in spite of their shared poverty. As with the field trip to the toy store, Sugar learns the lesson that Miss Moore wants them to learn. Sylvia also learns it, but her reaction is very different than Sugar's.