In season 5 of Leverage, Nate is obviously training Parker, Hardison, and Eliot to take over once he (and Sophie) retires.
In "The Blue Line Job" (S5E2), Nate asks Parker, "Well, how would you do it?" And in "The Gimme a K Street Job (S5E5), Eliot tells Nate, "I know what you're doing," referencing Nate's guidance in figuring out how to manipulate the members of Congress. But in "The Gold Job" (S4E16), Nate lets Hardison run the con and gives him guidance and encouragement when it fails.
When do Nate and Sophie (probably) actually start to train the rest of the team to take over after they retire? Season 5, or earlier?