I'm training as an ATC gliding instructor @ Kirknewton. It's a voluntary thing and you can either go in as civvy or apply for a uniform post on the school. It's a big commitment (I've been involved with ATC for 30 years and only in last year gone to a gliding school), which is on top of the 2 nights a week I already do at a Squadron.
Get in touch with your nearest ATC Gliding School (from your profile, can't tell where you are, otherwise I'd have suggested one and could have found contact detals for you!). Try a look at
HQ Air Cadets to find the nearest one to you.
HTH