I remember being taught possessive apostrophes and plurals very clearly. 2nd year juniors in the 1950s. Several examples, clearly explained and demonstrated on the blackboard, then some examples to copy and complete, then an exercise from a text book. Stayed with me for life.
My parents were always insistent on correct grammar and spelling, yet both had left board schools at 14. I have a large collection of postcards from pre-WW1 belonging to my grandmother, mainly from her large family, all educated at the local village school. Yet to find a spelling mistake in the messages.
As a primary teacher I do remember the spelling and grammar don't matter in the seventies and eighties; it is all about communication. Not in my classroom.