A wireless microphone system comes with two or three components. A receiver plugs into an audio mixer and receives the wireless transmission. A transmitter sends the signal through the airwaves. A separate microphone and wire connects to the transmitter. Wireless microphones can be hand-held, lavaliere, which clip, pin, or tape onto a lapel, tie, or wig, or over the ear. Your school will probably want a mixture of the three.
The first choice you must make is how much of your theater budget can be spent on microphones. Wireless microphones range from $200 up to thousands of dollars per system. Most schools don't have the budget for high-end microphones and, truthfully, don't need the extra features. You should also consider the potential wear-and-tear and maintenance costs on microphones and other theater equipment. Cheaper microphones are more prone to clipping, when the audio cuts in and out, interference on the frequency and other problems
Microphones come in several varieties and you must be the judge of what your budget, quality demands, and technical experience can support. VHF microphones are generally cheaper than UHF microphones but are subject to interference from a more common signals. VHF systems also have a shorter broadcast range than UHF systems.
Some microphones come with the ability to change broadcast frequencies to avoid interference. While a nice option, it does increase the cost of the mics.
Two favorite options of freelance audio engineer Clarence Davis are the Sabine SW70-H15-U-M1 and Shure UHF R series microphones. "The Sabines are really easy to just 'plug and play,'" says Davis. "They're a good choice if you're looking for a quick and easy setup. The Shures have a much better sound and are rock solid for all kinds of uses, but more expensive."
Call local audio engineers who know your specific needs and limitations to make recommendations. They can make sure you won't experience interference from other wireless transmitters in your neighborhood.