On Teaching Young Children
There is a concept that has helped me in formulating a method for teaching young children that is called the Integrated Maturity Level (IML). This refers to the physical aspects of a child’s' development such as all the muscles that control the eyeball, fine motor control, hand/eye coordination etc, and the brain's ability to integrate these systems. This integration is necessary in order to play any instrument. Some instruments are less "physical" than others and so would be easier to start on at a very young age.
The guitar however, is more physical than say, the piano. That is, it takes more brute force to squeeze a guitar string than to depress a piano key. Therefore, the level that the child is at in terms of the physical development is more of an issue.
In general, (very general) the brain does not fully integrate these different systems until age 9 to 11 for girls and age 11 to 13 for boys. What this means to this discussion is that if your child is taking guitar lessons before this integration happens he or she can play the right notes, can retain the knowledge, and learn all kinds of things but will not have the coordination to keep time and sound musical. When the integration happens, it is a relatively sudden thing and almost overnight the student starts sounding "musical." Countless times I have started a student at age 8, 9 or 10 and taught them for a year or two. Then at a certain point in time this integration happens, things start to sound like real music and the student progresses more in 6 months than in the 2 previous years.
The implication of this for me as a teacher is this: If the child has not had the integration happen, (I can tell in 2 minutes or less) my job is motivation. Give the student things that are achievable, keep it fun and at the same time impart knowledge and concepts that the student can take full advantage of later. If the child continues to be motivated, if he (or she) picks up the guitar and plinks around on it every day with little or no pressure from you, the parent, then it's worth it to continue the lessons and wait patiently for nature to take its course. If you have to remind the child and pressure them constantly to practice then you're wasting your money.
So, if your child is young (9 or 10 or less) keep in mind that they may not sound musical right away. This is not a reason to opt out and it doesn't mean they're not getting anything out of it, it just means that integration hasn't happened yet. If the child is self-motivated it's worth it. If the child is not self-motivated, wait a year or two and try again.