Windsurfing has definitely taken a solid back seat to kiteboarding, so it is actually a bit more of a challenge than it was, say, 10 years ago.
That said, one of the best places to learn is Boardsports School in Alameda, CA: http://boardsportsschool.com/win…
Located in the middle of Alameda's Crown Memorial Beach, Boardsports is a great place to learn a wide variety of surf-related sports (including the aforementioned kiteboarding, and stand-up paddle boarding) – the combination of the enclosed bay, plus a water depth of no greater than 5-6 feet even a few hundred yards from shore makes for an ideal training ground.
The main difficulty, in fact, is the irregularity of available wind power as compared to a coastal launch point. Still, it's a rare weekend that you won't find windsurfers and kiteboarders in abundance here, zipping back and forth, learning various tricks, and just generally having a good time.
Tell them Dean sent you, and watch their puzzled look as they haven't a clue what you mean.