Climbing lends itself to the Scouting model of requirements & checkouts, and segments of our climbing progression rely on this method. While everyone associated with the program knows the rules for requirement signoffs (right???), it’s worth emphasizing… nobody gets "signed off" until they can demonstrate the skill on their own, with no hints or prompting, in the real environment where it is used, at least one week after the last time they saw the skill taught or demonstrated.
For critical items (belaying, rappelling, climbing MB, anchor construction, etc.) the signoff is really "I am comfortable that this kid can do this activity without direct supervision." Just because a boy belayed properly through one rope doesn’t mean that he’s good to go for a belay signoff. You must consider temperament, attention level, etc. Have you seen him catch several falls? Be stuck on belay with a "stuck" or hang-dogging climber? Our usual routine is not to sign off on critical skills until we've seen boys work through the skills a dozen times or more without error, in a variety of environments, with deliberate distractions. This is very different from what has become common in climbing gyms, where typically youth and adults are allowed to belay after a short class and pro-forma checkout.
Remember, throughout the instructional process you must be aware that kids will generally expect you to do everything for them, from tying knots to ensuring their safety. Build in exercises to work against this attitude and make them responsible for their own and each others’ protection. Troop 8 practice is for adults and older boys to occasionally set up improper rigs during field work to "test" scouts attentiveness. An example would be an adult belayer with the belay mis-rigged; if the boy does not catch the problem during his double-check of the belay system, he’s "dead" and someone else gets to do the climb. This goes a long way toward breaking the spell of "magic" adult leadership taking care of them, and makes scouts remarkably attentive to each other and the safety systems.
In Troop 8, earning Climbing merit badge is used as our threshold of "this scout is now capable of doing simple things on his own." Thus a scout with Climbing MB is permitted unsupervised belays, regular rappels, etc. At this point, they are ready to start developing real climbing skills. We make a second distinction with those who earn their "first lead" award; these boys are capable of placing protection, building anchors, making safety and route selection decisions without direct supervision. Third level for us is "trip leader," where the person must demonstrate supervision and vertical rescue skills.