Should my child take half hour, hour, or longer lessons?
I once had two parents as clients who asked that I take their five or six year old child through a ‘music boot camp’ for an hour and a half each session (contrary to how it might sound, these were not hardened marines but rather accommodating parents who seemed exhausted by their child’s rebelliousness). I recommended they have their child take ½ hour lessons (and save money) since, in my experience, even that half hour will on average be spent being musical for 15 or 20 minutes and being distracted for the balance of time. I have found that an hour long lesson for a child does not generally yield much more time experiencing music but more time in distraction and less chance the child will find the experience of music enjoyable. There are definitely exceptions where a particularly cogent child under age 10 or one who has developed some passion for music will take an hour or, occasionally, longer session that is worthwhile for that particular child.
As a general rule of thumb, if the child is starting in music (i.e. exploring an interest in music), a half hour is appropriate for children up to the age of 12 or so but some children from age 9 or 10 and into their teens with a stronger passion for music (or having developed one in earlier musical learning) will greatly benefit from hour or hour and a half sessions, particularly if they have goals to explore more than one instrument (e.g. singing and guitar, singing and piano, etc.) or songwriting.