There are many ways to get an Undergrad degree without going to a mixed college. Desirable Graduate programs are pretty much all co-ed though.
Having in mind that degrees take 2-5 years to get, depending on credits received from previous sources, this means that within 2-5 years of going to a co-ed school, the boy/girl will be working in a mixed environment anyhow, so what are we accomplishing by holding them back from attending mixed colleges, when neccessary for their desired degrees.
Girls who dont go to college altogether, end up working in a co-ed environment sooner (offices) because they don’t all want to be teachers.
Some say that a few years later when the Singles have married and are more mature, there is substantially less danger of going to a co-ed College.