I have worked with the STEP/STAR program which provided some high school courses via television broadcasts. It is necessary to have someone in the classroom to do classroom management, assist students with getting help, and keep grade records. It does not work to just have the students watch the class; they need to interact with the teacher and with the assistants available to help with homework. The teacher in the studio does not know if the students are paying attention and/or if they understand the material. When I was in the classroom, I needed to be sure that the students WERE paying attention and then being sure that they asked for help if they needed it. 
Programs like this and courses on the internet are great, but they only work for motivated students and are usually for specialized classes like foreign languages and advanced classes. They rarely serve elementary and middle school students or provide basic courses for high school students, especially those who are struggling.