This is the best list I've been able to find for Sportbike training classes: Sportbike Riding Schools from Thirty or so classes all over the country.

For riders who want to go fast, there's no better place to learn than on the racetrack. Get some valuable track experience with these riding schools, many of them taught by former professional racers.

I'd add, learn to go fast, and you'll go slow a lot safer.

Here's a description from the Yamaha Champions Riding School, at Miller:

We help riders who want to improve their bike control—the racers looking to drop 1.5 seconds from their lap times, or the street rider who needs to miss the surprise gravel mid-corner… with a car partly in their lane. We coach new riders coming off of dirt bikes, the rider trading his cruiser for a sport-touring bike, the racer looking to progress to the national level or the track-day rider who wants to run in the A group. Many schools shuffle students through an assembly-line process that resembles nothing more than a track day with a few tips thrown out. Not us; we keep the student count low, and the instructor count high.

A buddy of mine wrenched for the Skip Barber school for the Formula Ford cars. The said it was a total blast... I always wanted to tag along some weekend.