Emphasise the difference in hand position from start to finish. At the start both hands should be facing inwards with thumbs pointing upwards. Then during the motion of the pass itself the hands should pronate (twist inward) so that the thumbs are pointing down. Also, you want to try and get the pupils to step into the pass with either foot, they can practise with both sides and see which is preferred for them, but it is worth learning both sides. A drill for this could be to use a wall if available, find a way of marking the wall, and allocating different points to different spots.