Clearly we must have been ahead of the game up here in the Nottinghamshire Coalfield during the 1940s/1950s! There was no classroom or playground segregation by sex throughout my time at Infant and Junior School, and indeed there was none in the Senior School on the same site except for activities like domestic science and metal work.
Each school had its own playground, or rather an allocated area of the large concrete playground which occupied three quarters of the area round the Junior School building. The house and garden of the Headmaster of the Junior and Senior Schools and the Infant School Building filled in the other quarter, and the Senior School buildings were on a plot stuck on one side.