Although no one believes that he will actually go through with it, Leper is the only one of the other boys who actually steps forward with the intention of jumping from the tree. Until that time, only Finny and Gene have done it, and they repeat the feat at the beginning of every meeting of the Super Suicide Society. The "half-dozen friends" who have shown interest in the club are only "signed up as 'trainees'". They remain anonymous, a nameless crowd; Leper is the only one that stands out (Chapter 3).
Leper's reaction to leaping from the tree foreshadows his reaction to the all-pervasive war. In both situations, he remains quietly on the sidelines, never fully involved with what the others are debating. Just as the others ask questions about the Super Suicide Society but never quite commit themselves to becoming full-fledged members, so they brag and bluster about how they are going to join up to fight in the war, yet in the end, it is Leper who inexplicably steps forward first. Leper is the first, after Finny and Gene, the founders, to volunteer to jump from the tree, and he is the first to actually make the move to enlist in the armed forces.
Leper does not have the strength of character to complete the challenges he faces. No one believes he actually will jump from the tree, and when he joins the army, he quickly learns it is not what he envisioned and is completely overwhelmed by the reality of it. Still, in both cases, he is the only character to move beyond the hype and attempt to put his words into action.