Actually, more is true: Catalan is the main language in the schools in Catalonia, the language used to teach all subjects (except Spanish, English, etc.).
The Catalan School System is designed to allow all children to become proficient in Catalan and Spanish.
At the University level, professors and students are free to use Catalan or Spanish. This is each one's choice.
Many Catalonians are afraid that this status quo is not good enough to guarantee the survival of the Catalan language, since Spanish has still a much stronger quota in the media.
It is sad to see how the Spanish government is jeopardizing the Catalan School System all the time trying to reduce the role that Catalan is playing in our education system. Many Spanish people would like to put Catalan out of schools, as it was for forty years during the fascist dictatorship of General Franco.