I find it very curious that people bandy around "good teacher" and "crap teacher" so freely. One size does not fit all.
My DS was at a selective, independent boarding school. We only got one chance in five years to meet subject teachers (as opposed to Housemaster / academic tutor etc) so I was intrigued to meet his teachers just as he started his A/S year. We were to meet 8 teachers. DS told us in advance that he did not know 3 of them, 2 were OK (and got good results) and 3 were "legends".
Legend One was mid-50s, donnish with a sardonic turn of phrase. A PhD. A world expert in some obscure part of his subject. Published. Not interested at all in the pastoral side of teaching. Extra-curricular stuff was behind the scenes - Library Chairman etc. Top set boys were in awe of his erudition and loved his lessons.
Legend Two. Late 30's woman. Feisty. Feminist. Again, not particularly interested in teenagers per se. Passionate about teaching her subject. Really lively, stimulating lessons.
"Legend Three. Early 30's man. Joined the City after university. Made a million or two by 27. Re-trained as a teacher. Ambitious. Interested in the wider issues of developing teenage boys. Good at the pastoral stuff. Will end up a Headmaster. Lessons OK but the man was a legend as a games coach. Charismatic and hard taskmaster.
Are Legends One and Two "crap teachers" because they have limited interest in their pupils beyond extending their brains? Is Legend Three a "good teacher" because he is an all-round educator (despite being only OK in the classroom)?