If you are attempting to pique a potential reader's interest in these two stories without giving away the endings, you might begin by addressing the rather ordinary beginnings. Both stories start by describing things that seem relatively mundane. In "The Lottery," a town gathers for some local tradition. In "The School," a classroom gardening project has gone south when all the plants died. Then, you can begin to give some clues that things are not as they appear in either story and finish with some mysterious reference to the stories' endings that will make a reader want to seek out the story him or herself.
For "The Lottery," for example, you might first describe the idyllic village setting, neighbors who treat one another like old friends, and their folksy appreciation for tradition. On this particular day, however, there seems to be a mood of uneasiness, of concern; folks seem a bit less patient than usual and no laughter is heard as the town gathers together. They are, apparently, gathering for a local tradition called the lottery. Now, typically, lotteries are something that we want to win, right? This lottery, on the other hand, is something none of us would ever want to "win." You might reference this irony in order to interest a potential reader without giving away the ending. Perhaps you could suggest that a gruesome irony alights on "the winner" of this lottery or something to that effect.
For "The School," then, you might first describe the narrator's humorous depiction of a number of failed class projects: the orange trees that died unexpectedly (all of them), the snakes that died when the school experienced a strike, the herb garden that must have been overwatered, the tragic but not unexpected demise of the tropical fish and the accidental puppy. But then, there is a shift in mood when the class casualties become human: a Korean orphan, parents of students, two schoolmates, and so on. Another shift occurs when the children begin to ask their teacher, Edgar, the narrator, about the meaning of life. The story goes from comedic to tragic to absurd when the kids start posing existential questions. The children, have, apparently, developed quite a depth of knowledge about one of the main things adults try to protect them from: death. And then they begin to ask probing and awkward questions about sex: the other big taboo. You might allude to the children knowing more than they seem to, being less innocent than the adults around them believe, as this certainly sounds rather sinister. The narrator does admit that he is "often frightened," it seems to us, most significantly of the children themselves. His fear and lack of insight combined with their evident peculiar, even absurd understanding of what has value in a human life ought to pique a reader's interest.