A mechanism for conjointly operating a plurality of gate assemblies mounted on a hopper car having an elongated car body with sides and ends, and a bottom defining a discharge area comprised of a plurality of discharge openings. Each gate assembly includes a slide door arranged in operable association with one of the discharge openings. The mechanism operates the slide door on all the gates conjointly relative to each other. Methods for controlling the gravitational discharge of material from a hopper car are also disclosed.