This might seem obvious seeing as the two, while similar in many respects, are very distinct languages. However, as someone who has only ever studied a language in a classroom setting, the marked difference I feel, even after only a few days, between learning French in school and learning Spanish in Mexico, comes as a big surprise.
I'm a book learner. It's how I've defined myself over the years (and probably why I am currently in grad school rather than a professional something-or-other... although I eventually want to be a professional something-or-other). While my grandfather, mother, and sister have all at various times learned a language simply by listening and speaking and interacting, I've always maintained that I need to study the language to learn it -- that is, I need to know the verbs, study the conjugations, the tenses, understand where to place adjectives, etc.
Yet here I find myself in Mexico with some basic vocab thanks to a brief introduction to Spanish back in sixth grade, but no real understanding of the underlying principles of the language structure and... whaddya know, I'm kind of speaking Spanish!
Of course, my Spanish is nothing that a real Spanish-speaker would be impressed with, nothing that could even really get me through a day of exploring Oaxaca on my own. But this whole new way of learning is what excites me, realizing that I know what "como" means, not because I read it in a book or looked it up in a dictionary, but because I've heard it in context several times now, and figured it out for myself. To be fair, I picked up a "Spanish Step-by-Step" book at the used bookstore before I left, and it's actually been very helpful so far, but even that book takes a fairly loose approach to teaching grammar and structure, relying more on example conversations to teach basic vocabulary and sentence constructions. And Spanish classes started today, which is actually a bit of a relief, to think that I *will* learn those grammar rules and practices that I'm currently missing in my rudimentary attempts to put together a comprehensible sentence from the ad hoc terms I've picked up here and there. But as I listen more and more to the Spanish that surrounds me here in Oaxaca, I realize how much I am picking up just from being here and wanting to understand what is going on around me. It also makes me realize that it's not as simple as just going to a country and listening in -- you really have to have these conversations and interactions constantly going on around you to pick up on what's going on.
At the risk of sounding narcissistic and self-centered, I'm really enjoying seeing my personal process of learning Spanish unfold. And, though I am enjoying Mexico and am excited by this introduction to a new language, it also makes me wonder where a similar immersion experience in a French-speaking country could take me.