I too saw it in Year 11 English in 1992. I remember the very slow motion rolling head. The witches made the biggest impact at the boys' school, where most of us had been since the age of 9.
Similar to my experience, only in '76 the entire year was taken on an excursion to the local art cinema to see a screening. Some of the English teachers were mortified by the nudity and our reaction to it (much cheering and whistling!).
It remains my favourite Macbeth film for many reasons. And yes, the sword fight at the end is excellent.
Some years later I was studying Shakespeare in the Cinema at university. After sitting through many impressive but overly long and stodgy black and white films I suggested to the lecturer that he should consider including Polanski's Macbeth in the course. He declined with the comment "But that was made after 1970."!