Grabbing a book and reading also works. The thing that a school gives is a standard curriculum so that a student doesn't miss concepts they may simply not know about.

I did things a bit opposite of who you are responding to though. In undergrad when I did my CS degree, I also did business classes on the side (economics is simply interesting to me). I ended up only a few classes away from an undergrad business degree when I graduated. Later I went back and got my MSc in CS.

The business knowledge I gained from those few classes early on has helped more than anything else in my career.