I cannot recommend Instituto Hemingway Spanish School enough! I spent several months taking group lessons with a couple of different instructors. Both were excellent at teaching and had terrific, warm personalities. With their help, my skills improved dramatically in a relatively short period of time.
I arrived at the school knowing only a few words of Spanish. I took 4-hour lessons per day Monday to Friday. This concentrated learning approach was extremely beneficial for me, and the school's location in historic Casco Viejo made it ideal for immediately applying what I'd learned in the neighborhood's array of shops and restaurants.
My time there was an absolute highlight of my extended stay in Spain.