There are private schools all over the place. They usually run anywhere from $1,800-$5,000 pesos a month. In addition to buying uniforms, at the beginning of the year you also pay an enrollment fee, an activities fee (around $2,000 pesos each), or you can look for a state school (some are good, some are bad) that costs around $500 pesos for the entire year.
If you are a student, ask your school if there are classes or tutors.
Local universities such as the University of Guadalajara (U de G) and the Autonomous University of Guadalajara (UAG) offer Spanish classes for foreigners.
Private companies include:
Pablo Neruda #2914, Col. Providencia, Guadalajara
Lopez Mateos Sur #2380, Col. Ciudad del Sol, Guadalajara
Hidalgo #1420, Col. Ladron de Guevara, Guadalajara
Donato Guerra #180, Guadalajara 44100