I think one issue here is whether a person needs to attend the school as a prerequisite for something, or just wants the knowledge/experience. In the outdoor organization that I volunteer with, such classes often are required in order to be allowed to "graduate" in some other skill area, which in turn is required to be allowed to go on trips with the group.

Something interesting that I learned was how they sometimes handle "equivalencies". I.e., you claim that you already have the knowledge; do you have to take the class? For navigation, they passed me on that if (and only if) I helped to teach the class (!). An interesting refresher for me, I guess, and interesting to see how well (and/or poorly) I thought they had structured their class.

For first aid, I find that they often need live human dummies for scenarios. Is it possible (?) that if you don't need to "have the class on your record" that you could volunteer in such a way and then hang around in the back to listen to the material, and then get the book from the library before or after?

There's certainly no substitute for having an experienced person putting things to you directly, and in context. But you can get a lot from books or websites so ... really tough to say, especially not knowing what kind of trips you aspire to go on, whether you want to hike solo or not, what your current level of experience and knowledge is ...