Lennart - I suspect that your perceived difference in the teacher's 'ability' had more to do with changes in you rather than the training provided at the teachers' college.
It could simply be that your teacher was better suited to the younger age group. Or perhaps, as a younger child you were more accepting and willing to engage with the teacher at that time.
I taught Math and Computer Science for many years and had experience with kids ranging from Grade 7 (12 yrs old) to grade 13 (17-18 yrs old). Having done so, it is clearly obvious that some teachers are much better suited for certain age groups. And, I contend that this has a lot more to do with personality than 'training' - i.e., the courses taken for the undergraduate degree and the follow-on courses at teachers' college.
I did not thrive at the lower (gd 7-8) levels - I simply could not relate well with their ranging hormones; but I worked with a number of [fantastic] teachers who could. I found that I was better able to work with the Senior level students. A number of my colleagues did not have the personality, confidence, background, etc. to work with that age group.
I had *tremendous* respect for people with the patience and personality to deal with the grade 9 & 10 non-academic math classes... teaching at that level has a lot less to do with knowledge of the course material than it does with understanding the audience and tailoring the delivery of the material to make it relevant to them. How you teach the course is highly dependent upon who is in the class (and their mood on any given day).
Last thought (I haven't read all of the other comments to see whether anyone else has raised it) - Einstein most likely would have been the wrong person to teach an introductory high school physics class... he would have had such a innate high level understanding of the material that (I'm guessing) he would not be able to describe it in simple terms to kids (some of whom are more concerned about when they'll get their next meal).