Greatbatch circuit
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The circuit that Wilson Greatbatch used was called a "blocking oscillator." Although the circuit is easy to build and replicate, it contains a component that can be hard to find and may cost more than is practical in a school setting. Instead, a simpler circuit costing about two dollars can be assembled to simulate the same effects.
The diagram below is the schematic for the oscillator circuit. The NPN and PNP designate transistors. The other four components are the resistor labeled 120k ohm, the capacitor labeled .47 uF, the speaker, and the battery. This is a complete circuit except for one final part. The last resistor was to be attached to the two open terminals labeled "RESISTANCE." This is where Greatbatch would have placed the last resistor. Parts list.
Assemble the circuit as shown in the photo below. In this example, the connectors are springs that have been twisted into a piece of tag board. Other options are to solder, twist the wires or use alligator clips to assemble the circuit.
To test the circuit, add the final component, the 10K resistor, then listen. Replace with the 1,000,000 ohm resistor. Listen.