Our respective experiences come, almost certainly, from different schools; quite possibly from different areas of the country; and definitely from different times. I started infants’ school in 1961 and moved to the junior school in 1963. Sometime during that year we moved across town so the rest of my primary education was in another school.
From what I remember of my first school, the infants’ and junior schools were separate but on the same site with their respective playgrounds separated by one of the school buildings. There was a secondary modern school on an adjacent site. I don’t know if the Sec. Mod. school was co-ed or single sex. There was no sex segregation in either infants’ or junior schools.