They need to try things out for themselves rather ripple tank just following instructions. Practical tips: See apparatus note Ripple tank and accessories for important details. When you ask whether the water moves along with the pattern, you could leave the students to devise their own tests and to think and experiment on their own, rather than giving detailed instructions.
It is worth considering where the dark and bright ripples come from. The convex and concave surfaces on the top of the wave make perfect lenses. When the light falls on the surface in the ripple tank then light is either focused by a convex surface or spread out by a concave surface. The concentrated light produces bright bands. It takes time to set up ripple tanks properly.
If you are going to use a set of ripple tanks for a class experiment, you may want to leave them on a side bench between successive lessons. Or, if the lesson follows lunch or morning break, you could ask a few students to come early and help set them up. For demonstration purposes, you can now use a compact ripple tank designed to sit on an overhead projector. This produces a large image on screen, which the whole class will easily see. Beware of water on the laboratory floor. Make sure you have a sponge and bucket handy to mop up spills immediately.