A great resource for mastering Spanish grammar on your own.
Learning a language must be approached on many fronts. The four main skills in any language are speaking, listening, reading and writing. I believe that a classroom is most useful for practicing the productive skills, speaking and writing. A good teacher will give you time to practice and correct your mistakes.
Reading and listening can be done on your own. You don’t really need to spend too much class time on these skills. Any newspaper can give you reading material and there’s a wealth of songs and podcasts on the web for any language skill level you need.