A vehicular slider window assembly includes a frame portion having an upper rail and a lower rail, a fixed window panel, and a movable window panel that is movable along the rails between an opened position and a closed position. A drive system is operable to move the movable window panel between the opened position and the closed position. The drive system includes a single flexible drive element that, when the drive system is actuated to move the window panel in one direction, the flexible drive element pulls the movable window panel along the rails, and when the drive system is actuated to move the window panel in the opposite direction, the flexible drive element pushes the movable window panel along the rails. The lower rail includes guide structure that limits flexing of the flexible drive element when the flexible drive element pushes the movable window panel along the rails.