I spent 3 weeks studying at the Spanish School, Tecun Uman, located at 6a Calle Poniente 34A in Antigua, Guatemala. It cost about $100/week for 4 hours a day for a private Spanish teacher.
My private teacher did not speak any English, so it actually worked out great. Any time I did not understand a word in Spanish, she had to define it for me in Spanish, which really helped my listening skills. My teacher was a Mayan woman, and was a fairly good teacher. She used materials from other schools and had a set plan for teaching (grammar and drills from 8am to 10am, reading and conversation from 10am to noon). The only complaint I had was that there were no books for me to check out and take home.
The school had places to sit in their main office, as well as in another location about 2 blocks away. Both locations were well-kept and clean, with free coffee and water. I would say that their facilities were not as nice as some of the other schools, but the view of the volcano made up for it. Also, when the school was really crowded, it became a bit noisy, as there were some 60 students and their private teachers speaking at the same time.
The school had a lot of activities, as the school director, Mario, was truly involved and cared about his students. There were free salsa classes once a week and cooking classes every now and then (I learned how to make a special Guatemalan dessert!). There were also trips to nearby towns (eg San Antonio Aguas Calientes, where you can attend a lecture in Spanish about the customs in the town regarding their textiles), museums, and other sights. All activities were very reasonably priced (not like some other schools, which were obviously making money on their activities). Overall, I would say that the activities were one of the highlights of the school!