Leslie moves to Lark Creek at the beginning of her and Jess's fifth-grade year, and she stands out in shining contrast to the rest of the students. Her parents are highly educated, intellectual, affluent, and liberal, and they have exposed her to the wider world in a way that none of the students at Lark Creek have ever imagined. Leslie is full to the brim with imagination, creativity, mischief, and fun. A voracious reader with a keen sense of intellectual curiosity, she is the one who comes up with the idea of Terabithia. She immediately senses the potential in Jess and the two become fast friends, and it is she who draws Jess out of the socially constructed shell that has constrained him for his whole life.
Leslie is also kind personally and emotionally. Unlike Jess, whose parents give the appearance of being too busy and careworn to devote much excess energy to raising their children, Leslie's parents—though not always, perhaps, the absolute most attentive parents in the world at all times—have nevertheless always had time for her when she's really needed them, and have given their best to bringing her up to make them proud. Under this wholesome influence Leslie has become an extraordinary child. Most of the students at Lark Creek, with their unerring instinct for absolute conformity, do not care much for her because she is so different, but she proves to be the perfect friend for Jess.
Leslie often gives the impression of being absolutely fearless, which Jess at once admires and finds intimidating. Jess has become convinced throughout his life that a truly admirable person is never scared of anything, and Leslie's apparently dauntless nature rubs on a sore spot in Jess's soul, for he wishes he could be the same way. However, as we see at the end of the novel, Leslie's fearlessness ultimately is her tragic downfall. Jess had berated himself many times for being afraid to swing across the creek when it was high, but then the rope breaks while Leslie is swinging and she falls to her death. Thus one of her most admirable characteristics is proven to be less than perfect.