I have been a medical transcriptionist for 12 years, 8 of them working at home. I go into my office 2 days a week to drop off work and pick up work. It does take a lot of self-discipline, and the isolation factor is something to take into consideration. However, I work while my kids are in school and it allows me to be there when they get home. My schedule is flexible; if there is a function going on at school during the day, I can be there. Also, having to stay home with sick kids isn't a problem.
I never had formal schooling -- I learned as I went along on my first job. Since then I have worked in many different medical fields; orthopedics, GI, neurology, podiatry,etc. Fields are so specialized today -- being well-versed in one field doesn't necessarily mean you can do any type of practice. There are schools all over my area, but two of the doctors I worked for wouldn't hire anyone right from school, as they wanted them to have some experience. There are a couple of different ways to approach it. You can work as an independent contractor and work for docs that way (which is how I started, because I specifically wanted to work at home), or work as an hourly/salaried employee, as I do now. Just keep in mind that working as an independent contractor means no benefits, vacation time, etc. If you take a vacation, you have no $ coming in for that period of time. It has become a bit of a cut-throat business, at least in my area, and there are always other people looking to undercut you price-wise.
I don't mean to sound negative about the whole thing -- I wouldn't have done it for this long if it wasn't beneficial for me. But, like someone else said, it is not for everyone. THere is a lot to take into consideration.