When I first went to the Dominican Republic, I remarked about how hard it was for me to completely understand conversations being overheard (not being slowed or annunciated for my benefit).
I continued, "... and I have studied Spanish formally in Junior High, High School, and at the University and I was the best student in every class, got staight A's, acted in Spanish plays, and was the Spanish Scrabble Champion at my high school. So if I have trouble, imagine how hard it must be for everybody else."
A young Dominican countered that she spent 3 months with her boyfriend living in Germany, that she picked up German in that short time, and that I must just be "slow". It's easy.
Of course I knew I wasn't "slow" and I knew where I stood in relation to other language students.
The point is, some would say I'm fluent, others would say not even close. It all depends on what each person believes is meant by "fluent", "master", etc. Hell, I'm an educated man and I can't even understand some AMERICANS the way they speak "English".
By the way, while I still cannot understand some Dominicans, I think I speak better "Spanish" than most of them. Now, define "better".
Nothing beats immersion. Nothing. School gives a good foundation.
I think 6 months of combination immersion and school will have just about anybody well on their way to being at least "conversational" in Spanish.
Most expats I know can hardly speak Spanish, despite living in the DR for 10 years. That's because they all hang out with each other. That's why even the ones that LIVE in the Dominican Republic often know so little about what is what. They know only what they tell each other, the blind leading the blind.
It's not uncommon for someone to come visit a city and in 1 week, know more about the city than some people that have lived there all their lives but don't get out much. For example, I was amazed to meet people that lived in NJ near NYC all their lives and had never been to Manhattan!