Knowing whether to start with rules or whys is a key to effective teaching.
I love starting with why in my teaching. “This is a problem we had. Here’s how we solved it.” It’s a great way to get engagement and investment in our students. When I teach the story and value of The Real Book, I start with why it was needed. When I used tuning exercises to help my students’ ears grow, It’s after I give a demonstration and explanation of why our tuning system is not perfectly effective for a cappella singing.
But sometimes, the best approach skips right over the why into rote memorization. Math students don’t need to know why PEMDAS must be in that order, because getting into the philosophy of mathematical syntax and touching on Gödel’s Incompleteness Theorem is unnecessarily confusing at the outset, though I would circle back with examples after I taught it. The same is true for learning key signatures. I think the best way is rote memorization. I can say “GDAEBF#C#” in about four seconds. If I circle back to explaining how key signatures are derived and why they are useful, it’s after I require memorization.
The right way to teach Concept A isn’t always the right way to teach Concept B, and in my experience, the way I was taught isn’t always the most effective way. I have had to reconsider, revise, or even trash some approaches that helped me learn: sure, they worked, but another approach is more efficient.