I have used the Hispaniola language school in Santo Domingo. It was OK. The teachers are all part-timers (just students earning a bit of extra money really) and generally follow the textbook pretty rigidly. But, like you I just wanted to brush up on my grammar, and because at intermediate level the classes are very small (most likely 1 or 2 students) and you can take extra individual classes, there are opportunities for more individually focused lessons (specific grammar issues, writing assignments, etc.). To improve reading skills I would just buy a book or newspapers and practice.