I've been teaching spin classes for several years. I try to gear mine toward cyclists who also ride on the road. I do tempo rides, intervals, LT workouts, cadence drills, you name it. Instead of getting in and out of the saddle a lot and resting every other song, I focus on strength and endurance.

We did the 2x20 minute AT test recently. It's nice to do on a spin bike because you don't have to worry about stopping for cars or signals.

Vary your workout so the students don't get bored. Give them options so the hardcore cyclists can work hard while those just there for an aerobics workout can take a break. Example: I do a time trial class where the students get their choice of three 9-minute trials with a 4 minute recovery in between, two 15-minute trials with a 5 minute recovery, or a single 35-minute trial. The hardcore people go for 35 minutes, the newbies do the 9 minute version.