But what is striking me right now as a math teacher is a passage from Kaiser's book, describing how the teaching of quantum mechanics in 1950s America had changed from pre-World War II era pedagogy. Prior to the dispersal of the European founders of quantum mechanics across the globe, they had had ample opportunities to argue, debate, discuss, and wonder about the philosophical implications of what they had invented-slash-discovered. Textbooks written in the 1930s included long philosophical asides on the interpretation of quantum mechanics. Famously weird phenomena such as Schrödinger's cat and the double-slit experiment became commonplace topics of conversation.
That all changed after the war, because physics was perceived as an applied field; it had helped win the war for the Allies, and as the Cold War became more heated, physics became more important. In order to keep up the supply of physicists, the style of teaching and the topics taught changed. From Kaiser:
Faced with such runaway growth, physics professors across the country revamped their teaching style. They began to accentuate those elements that could lend themselves to high-throughput pedagogy, pumping record numbers of students through their courses. First to go was the discussion-based, qualitative, philosophical inquiry into what quantum mechanics meant... A few years later, another critic [the physicist George Uhlenbeck] weighed in... he accused his American colleagues of confusing what was "easy to teach" - the "technical mathematical aspects" of quantum mechanics, which could be chopped up and parceled out on problem sets and exams - with the conceptual, interpretive material that students needed most. (pp. 17-18)
In short, the larger the class, the less time spent talking through the big issues at the heart of quantum mechanics... The quarter century during which this Cold War style reigned witnessed an extraordinary buildup of calculating skill. All the same, an intellectual trade-off slipped by unnoticed, with wide-ranging implications... The fundamental strangeness of quantum reality had been leeched out. (pp. 19-20)To my mind, this parallel is occurring right now in mathematics education. With more and more students taking more and more mathematics, we are devoting less and less time to investigating the strangeness within it alongside our students. We confuse what is "easy to teach" (that is, "easy to assess") with conceptual, interpretive material.
It required a bunch of frustrated young physicists in the 1970s to change the perspective of the larger physics community to any degree. And arguably, that philosophical way of thinking still has not re-entered the physics world, much to its loss. Calculation still rules physics, and it still rules math education. And when we lose math students because we've spent too much time on the "how" and not enough on the "why/what happened", that's an even greater loss.