There are IIRC 3 education authorities. Devon , Torbay and Plymouth. WIthin Devon - most of the county- I only know about Exeter and a few rural areas in East, west and south devon. In Exeter & East Devon most secondary schools are 11-16 , with a few 11-18 in East Devon.
Rural secondary schools in West devon as AFAIK south are generally 11-18, many offer NVQ vocational subjects as well as academic.
We moved from Exeter to West Devon partly because of schools, I wanted my son to go to an 11-18 school and not have to transition to college at 16.
Primary schools are harder to generalise about, in city and town schools you might find 90 kids in a year group, or you might find only 30 depending on the school. Some schools are quite mono cultural because of who lives in their designated area. Near the Universities you will find more ethnically mixed schools .
Have you had a good nose about on teh county education web pages? A lot of schools have websites too which give an idea of what their scale and resources are.
You haven't said what your sons statement is for or recommends he needs, IF he needs a school he can;t "escape " from easily, city/ town schools are more likely to be securely fenced than a small rural school, City location would also give you more options if you think it might take a couple of schools to find the right one.
House prices in the county are fairly high if your buying. Premium prices for easy access to the M5, Beaches or Moors.