The third semester I studied Latin in college was my first semester studying Italian. By the end of that semester, I knew more Italian than Latin, so I switched. I suspected that the ancient Romans had another language to do their actual thinking, since I figured all the grammar rules would get in the way of figuring anything else out. Learning Latin in elementary school would certainly be more effective than waiting until college (or 7th grade, for that matter).
Personally, I think that Latin instruction is over-represented in American schools and colleges. Cuneiform, Arabic, and Chinese are all underrepresented, as far as the relative utility of applying the languages versus availability of instruction.
As a history teacher, I do point out the Latin and Greek roots to my students ("Peninsula comes from the Latin paene insula, which means "almost an island"). As far as teaching it to them as a language, I do think it makes more sense to teach them Spanish. Depending on where they live, they may have many more opportunities to practice in an organic way and a better chance of the language opening up a new world to them.
