They would definitely not be boarding schools; you wouldn't send 6 and 7 year olds to boarding school. I would see McGonagall's school being a reasonable size, with four or five teachers including herself, and maybe 50-60 students ages 6-10, and it would be in some old stone house in a hidden, Magic back alley in Glasgow. I see Draco Malfoy's academy as about the same size, housed in a Georgian manor in London, and I still see a "public" (in the American sense) Wizarding Grammar School in London with a somewhat larger student body. Probably anywhere there were enough Wizarding families about, and someone willing to take on the role of teacher, there would be the sort of one-room schools Kat mentions.