There are times when I wonder what the issue is. if a scout is not "active" how does he move from Tenderfoot to First Class? There are events to attend, knots to learn, food to cook and tents to pitch and sleep in. If the scout completes the requirements, then he must have been active in some manner.
For Star to Life, there are merit badges to earn and POR's to complete. If the scout is not performing up to par, then there should be scoutmaster conferences on specifics and the scout needs to be apprised of what he is doing "wrong" and what needs to be done to make it right. Ed brings up an interesting point. if the scout is struggling with the quartermaster position and he finally "gets it" at the 5 month mark, its really not fair to those Scouts who were doing their job from say one to let the Quartermaster serve one month at the level of performance you wanted for 6 months. Now, if you let the youth continue to serve, he could get his 6 months in and then he has the time requirement in and that is that according to what I and others have said.
I think to be fair to all involved, if the scoutmaster wants the youth to serve past the six months mark, perhaps to 10 months before signing off on the youth's POR, I think a simple note of documentation would be good. Just somehting like a letter or a memo spelling out that the youth is expected to serve until some specified date at a specified level of performance to get credit for the POR. Both Scoutmaster and Scout sign and you have an agreement. This process is very similar to the process to be followed when a scout does not complete a Board of Review. A letter is sent to the scout outlining the actions needed before the next BOR which is scheduled in the letter.
Fathers, do not irritate and provoke your children to anger [do not exasperate them to resentment], but rear them [tenderly] in the training and discipline and the counsel and admonition of the Lord.