yes, it's brilliant. it's all about body alignment and poise, it makes a huge difference to ones riding. love it, can't recommend highly enough. who is taking the course, out of interest? I had sessions with Sally Tottle and she was absolutely excellent.
I have just come back from an Alexander session - not riding but for me.
I have had back problems since uni and have had what seems like constant physio, osteo and chiro sessions on and off for the last few years. Nothing seemed to really work long term and I had the feeling that a lot of it was down to my posture and me using myself wrong. We are slowly unworking a lot of bad habits and it is making a real difference, and I think it helps the riding too.
Edited to say - the AT sessions are hard to describe. It is not like you do any exercises as such. The lady I have helps me recognise which muscles are tense and helps me to work out how to relax them and to help me see how much body should be when sitting and standing, and just generally, ie how to get it back in balance. It is a very non-doing activity, but is highly effective. I tried explaining it to someone and they looked at me like I was mad and wasting my money.
I haven't found an AT riding instructor, but do have a ride with your mind lady, which is similar and again that has made a lot of difference.