Differential aileron is what you get when you rig your ailerons so their upward deflection of one is greater than the downward deflection of the other. It's most effective when the airfoil is a cambered one.

What happens is that downward deflection of an aileron on a cambered wing simply increases the camber. The movement basically alters the airfoil to have more camber in a somewhat gentle L/D progression. The lift increases gently as does the drag. On the other side of the wing......

The aileron moving up over on the other side of the wing starts to create a significantly different airfoil. As it begins to move, it somewhat radically turns that side of the wing into a reflex airfoil. It starts to lose lift. Less lift often results in less drag. That side of the wing has less drag and is held back less because of it. It moves forward as it moves down. Where would the nose go if that downgoing wing was moving forward? It'd move up. Where would the tail go? down....

Look that trainer over. Does it look like it'd do all that stuff? If its got a servo for each aileron, it's dead simple and easy to re-rig the servo arms and get differential.