Hi!
Also keep in mind:
Most catholic schools are crowded b/c they are the cheapest option if you want a private school. I have been looking for Catholic schools in the Belgrano area and it´s not easy! I have found a vacancy for my 4 year old (33 children per class with a teacher and and assistant) but my 6 year old is still to be confirmed (40 children, one teacher). Not very happy about it, but my priority was that they had "horario simple" (turno mañana o turno tarde). Most private schools have mandatory "doble horario" starting at 5 years old, which means kids spend an average of 8 hours in school.
Don´t worry about Catholic schools being old-fashioned or narrow minded. I´ve heard that nowadays their emphasis is more on Christian values and not so much in being perfect Catholics (except for the Opus Dei schools)
Jeez, I am making an efort with my English and now I re-read your msg. and find out you speak Spanish!
The schools I´ve looked at in my area: Manuel Belgrano, San Román, Instituto Santa Ana y San Joaquín, San Maximiliano Kolbe, Esclavas del Sagrado Corazón de Jesús and La Misericordia.
Saludos and good luck!