A 12:1:4 special education teacher will work with up to 12 students and one additional staff member (e.g., paraprofessional) for every 3 students.
A 12:1:4 teacher serves students with severe and multiple disabilities with limited language, academic, and independent functioning. These students require a program primarily of habilitation and treatment, including training in daily living skills and the development of communication skills, sensory stimulation, and therapeutic interventions.
You can find more information about 12:1:4 classrooms here.