There are a bunch of different kinds, the one I had back in high school had a wireless transmitter and receiver. The teacher wore a microphone and transmitter, and I wore a receiver that had a headphone jack, I had headphones that hooked over the back of my aids and transmitted the teachers voice directly to my aids in T-coil mode. It could also be used with regular headphones, but that wouldn't have done me much good. Some hearing aids come with a 'boot' that is attachable to the bottom. The boot is the receiver that directly picks up the teachers mic. There are several other kinds too.