Some teachers teach from life.
My piano teacher played the piano. Like, all the time. He had to; it's not easy to make a living as a musician. Between tours, his band played restaurants, bars, weddings, anywhere they could get a gig. He wrote jingles for infomercials and TV shows, produced tracks for hopeless hip-hop artists. He'd sit in twenty-hour recording sessions, driving home as the sun came up. He chose this life because he loved music, and when he taught music, he was teaching what he did. In that way, his teaching was honest.
My improv teachers perform improv. Not as a hobby, but as a centerpiece of their lives. I remember John Remak casually beginning a talk with, "I've been doing improv for twenty years, I love improv, it's my life." It's my life. John makes his living as an attorney, but improv is his life. He teaches from his own experience, and in that way, his teaching is honest.
Back in high school, I was taught differential equations by a working engineer. He spent his days at Lawrence Livermore Laboratory, and for whatever reason, chose to spend his evenings at the local community college. Differential equations wasn't some abstract arcana to him. It was his bread-and-butter, and he apparently found it important enough to share.
Same deal with linear algebra. I still remember the engineer/teacher (a different one) mentioning a poster hanging in his lab, created long ago by some exasperated colleague, stating in large block letters: "DO NOT USE CRAMER'S RULE". That anecdote was startling to me, almost shocking — after a full schedule of high school classes, this was the first hint that I was being taught something that was part of someone's life. Until that point, it hadn't occurred to me that anyone would use Cramer's rule.
Many of my college professors practiced what they preached. My information theory professor would teach me information theory in the morning, and then spend the afternoon furthering the field. Sure, what she taught was somewhat elementary by her standards, but she was well aware that this elementary theory was the foundation on which her life's research was built. It showed, and it stayed with me. A few years later, in grad school, I would make my mark by being the first to connect information theory to a seemingly unrelated problem in circuit design.
Traveling through Toronto recently, I met a man who taught plumbing at the local trade school. Inside his classroom he had built a house; this house had six bathrooms and nothing else. His students had been rejected by the mainstream school system, labeled "failures" for their unwillingness to sit still and memorize. He gave these kids a solid, useful skill, gave them confidence and pride in their skill, set them up with apprenticeships, and generally put them on the road to a decent life. These so-called "failures" weren't dumb. They came to this guy's House Of Bathrooms and listened up, because he earned their respect. Twenty years of plumbing had provided for a family and a home, he had run his own plumbing company, he literally knew his shit. He was as much a role model as a teacher; these kids learned his skill to earn his life.
I can hardly consider myself a teacher in comparison with these people, but when I write or talk, it comes out of trying to understand a way of thinking that's deeply personal and valuable to me, and then trying to share this understanding. It's more than mere passion — anyone can be passionate about anything. It's a kind of honesty that comes from distilling and passing on my own genuine insights and experience.
Okay. Now, let's think about the sort of people that we typically think about when we hear the word "teacher". Say, high school teachers.
I might believe there's a history teacher who spends her evenings reading contemporary accounts of the civil war, or a writing teacher who submits short fiction to the local literary journal.
But how many high school calculus teachers spend their evenings doing calculus? (What would that even mean?) Can you imagine a geometry teacher spending his evenings writing faux-formal proofs with modus ponens? Do algebra teachers even use algebra? Do they depend on it?
Can you trust a teacher who doesn't use what he teaches? Who has never used what he teaches?
Can you trust a teacher whose only connection to a subject is teaching it?
How can such a teacher know if what he's teaching is valuable, or how well he's teaching it? ("Curricula" and "exams", respectively, are horrendous answers to those questions.)
Real teaching is not about transferring "the material", as if knowledge were some sort of mass-produced commodity that ships from Amazon. Real teaching is about conveying a way of thinking. How can a teacher convey a way of thinking when he doesn't genuinely think that way?
I'm sure many teachers spend their evenings thinking about teaching the subject. I have no doubt that these teachers love teaching, and love their students. But to me, that seems like a chef who loves cooking, but doesn't love food. Who has never tasted his own food. This chef might have the best of intentions, but someone in need of a satisfying meal is probably better off elsewhere.
See also Paul Lockhart: Mathematics is an art, and art should be taught by working artists, or if not, at least by people who appreciate the art form and can recognize it when they see it. It is not necessary that you learn music from a professional composer, but would you want yourself or your child to be taught by someone who doesn’t even play an instrument, and has never listened to a piece of music in their lives? Would you accept as an art teacher someone who has never picked up a pencil or stepped foot in a museum? Why is it that we accept math teachers who have never produced an original piece of mathematics, know nothing of the history and philosophy of the subject, nothing about recent developments, nothing in fact beyond what they are expected to present to their unfortunate students? What kind of a teacher is that? How can someone teach something that they themselves don’t do?
See also John Taylor Gatto, and his ideas for communities where every adult is expected to contribute to teaching, as a form of civic responsibility.
See also John Holt, because everyone should see also John Holt.