Sautillé can be a serious business - notice the concentration when two teachers work together!
To develop the rebound for the up-bows we can practise with an interim 'wall' to bounce off. Hitting the leg is useful if you are seated (it is soft and does not hurt too much!), and hitting the hand as shown here can be used when standing.
It is important for students to realise that the basic sautillé stroke is easy. Simply change the angle of the stroke from détaché and you get the sautillé effect. Do this on the student's violin so the student can see and feel what the sautillé stroke is like close-up.
It is also good for the student to play the left hand alone and realise that the left hand coordination has to be good for a sautillé stroke to work.
As with all bowstrokes, point of contact is important in sautillé. If the bow is slipping across the strings (e.g. towards the fingerboard and back towards the bridge) then work on maintaining your point of contact. The student can see this clearly when watching the teacher move their bow.
The image of a wall in the game of squash is useful - one player hits the ball to the other by bouncing it off the wall....