Long slinky springs (much longer than the 70s toy) are available from lab suppliers for this specific purpose. They can be used in the classroom in a variety of ways as mentioned in the experiments below.
Longitudinal and transverse pulses
Lay out the slinky and attach one end to a lab stool or other fixed object so that you are facing it end-on. Take the other end and quickly move it about half a meter to the right and then back to the centre to create a transverse wave pattern that should travel along the length of the spring. Compressing the spring about half a meter then extending again will create a longitudinal or compression wave.
Motion of an individual turn
Teachers may want to demonstrate the individual movement of a turn of the coil. Marking one or more of the turns with a piece of tape clearly shows this single movement.
Speed of waves
By altering the tension in the spring and amplitude pupils can investigate how this will affect the speed of the wave.
Fix one end of the spring tight and move the other end as in experiment one. As long as the friction from the floor is not acting too much upon the spring movement, reflected waves should return along its length.
Send a pulse from each end at the same time and look at the resulting effects. Either the wave will cancel out or double depending on the polarity of the movement.
Pulse the spring at even intervals until the wave pattern becomes stationary.