In my experience, most people think they know the cause of the seasons, but a lot of them are wrong. Some think the Earth is closer to the Sun in summer, but this cannot be true because otherwise we could not have summer on one point of the Earth at the same time as winter on a different point. Some think that particular parts of the Earth are closer to the Sun in summer, making them warmer, but this again is incorrect. The distance between the Earth and the Sun is far larger than any small variations in how the Earth is aligned.
The actual cause of the seasons involves abstract thinking. In the winter, the tilt of the Earth is such that the Sun’s energy is shared over a much larger area of the Earth’s surface than in the summer.
Why does this matter? Because highly intelligent adults often have misconceptions such as these ones about the seasons and the only way to get past them is by gaining specific knowledge.
Similarly, the same adults could have misconceptions or lack knowledge about reading instruction or mathematics instruction, despite being otherwise highly intelligent. It therefore seems clear that secondary teachers need a good grasp of the subject they teach and primary teachers, who are often generalists, need a good grounding in all foundational areas.
Yet, when you look at the research, it is possible to conclude that teacher knowledge does not matter. Typically, such research uses the proxy of additional qualifications and compares the effectiveness of teachers with, say, a masters degree with those who do not have one.
One such study is instructive. Conducted in North Carolina, it makes uses of that state’s extensive data collection and does indeed show that teachers with masters degrees are no more effective and, in some cases, are even less effective than those without.
But wait a second, this argument was about specific knowledge and we may have fallen in to the trap of assuming the existence of general skills and abilities that don’t actually exist. Why should writing essays about neoliberalism or Freire stop you from holding a misconception about the seasons?
And if we look at the North Carolina study in more detail, we can see that the researchers examined a number of factors other than masters degrees. North Carolina also requires teachers to sit licensure tests that assess their knowledge of the curriculum. Higher scores on these tests do correlate with more effective teaching.
So yes, teacher knowledge matters, but only if it is relevant to what they need to teach.