I think it can be done either way, but going sans school is tough unless you're extremely disciplined and have a good natural business sense. That being said being in a GOOD school is paramount and unfortunately when it comes to design and photography there are a lot of racket schools out there.
I will never forget the day I wasted 20K on total crap teaching. I went to school originally to become an illustrator and a web designer. Photography was a secondary thing, and I went in with quite a bit of knowledge from reading a lot, having taken quite a few art classes in high school and with a fair idea of how to use Photoshop, Illustrator and the like for the basics.
Their idea of a comprehensive 2 year degree design curriculum? 2 semesters worth of very basic art history, painting color comparisons by hand, playing with shapes and noodles, and finally taking some barely competent digital imaging classes using only Apple computers and versions of software that were 2 steps back. 3rd and 4th semester? A little more drawing, some more painting, no illustration, and nothing more advanced in terms of learning to do proper illustration, etc via computer. No basic HTML, nothing about coding for web, making web graphics, nothing, else, just the above.
That was supposed to prepare me for working in the design field?
NOT
I left there, 20K in debt, and a lot wiser, went out to the West Coast, started teaching myself the more advanced tech stuff from books and videos, and while NOT working in my chosen field, finally found a decent photography mentor, or rather he found me, but that's another story.
Honestly I think 75% of what I know now, and for the record I have quite a ways to go, I'm not pro material, not yet, and I freely admit that, I taught myself. But that other 25% the GOOD stuff I got from my first mentor that was just invaluable.
If I had to do it over again I'd just learn the tech stuff myself and only take classes in photography one at a time. No college, no design school just good tech classes, seminars and such focusing more on the things I really want to learn. I'd still study with my mentor if I could. Taking the to spend learning with him was the best decision I ever made, and I really regret that I had to leave before I got to finish with him, but I'd definitely go back and just forget the college and formal design school.
There are other places you can take photography classes. Most bigger cities have art centers with photography classes and labs, mentor programs. That's the route I'd go if I could. On top of that there's always video tutorials, and seminars. It's a much more effective use of the money than college for someone who wants to be a good pro photographer I think.
That's not to say you can't do it yourself, but I do think it's harder. A mentor, classes, it does help keep you focused.