well, thev, my mother just recently did an editing/proof reading course. there was guaranteed work at the end, and it seemed to be that you did that for 6-12 months and then could use that as your experience to put on your c.v. for applying for jobs.

there was some sort of proficiency type thingo to get into it - they sent a bunch of stuff and gave directions of things to look for/correct. unfortunately she's not well and ended up not completing the course, but she found it wonderfully stimulating etc because it was online/computer type editing, but also the old fashioned way with a red pen and a series of codes - not unlike shorthand. there were also discussions about style etc.

i'm sure if you googled and asked at colleges you'd find a few options - especially for the states.