Why Isn't One Hour of Sunday School a Good Idea?

Many think that one hour of Sunday school can accomplish anything lasting in these young lives so saturated with other media all week long. It gives the impression that life changing impact and influence is directly proportionate to the quantity of time spent under a particular influence. Paul taught that we ought to do only those things which build up rather than tear down. What I have in mind here is tremendously encouraging for teachers, but all those involved in any kind of counsel or advice or ministry of any sort.