Many guitarists, especially adult students, get really caught up in doing everything technically perfect. They try to do each movement precisely as it can be done, and buy books and books on technique and exercises. I know this because that was me during undergrad. I read a lot of books on technique, and learned a lot. But I got so caught up in trying the newest things I’d read that I didn’t really give anything any time to work.
Teaching a young child guitar is interested. After they get playing, they just enjoy it. Teaching children is really about their selective ignorance. The techniques a teacher gives them become their entire world: it’s the only thing the student knows. And over the course of a year or two the young student develops and a good teacher can help guide that student as their technique grows and is refined. You don’t throw a treatise on technique at them and say, “Do all that by next week. Thanks.”
Perfect technique from the start is a not going to happen. So do some technical work and think carefully about it (practice what you suck at). But really it’s about getting the big things correct and playing some music. The big things meaning basic correct movement patterns, good posture and relaxation. Refinements should be added in later.
In my mind that’s were books like Shearer fail. There’s simply too much information. A student reads all the things, and then tries to implement them all at once into their playing. But it’s impossible. No one can tackle doing that many things all at once, let alone someone who is still trying to develop the basic coordination required for playing the guitar.
Don’t get so caught in perfect technique.