In reply to Flying Spaghetti Monster: Tricky. What do you want? A 3 hour session? I teach outdoor climbing. About a third of the people I teach can belay safely after 10-15 minutes. That doesn't mean I'm not there providing additional safety. But some people can and do get it consistently right after 10 minutes. The problem comes after that session ends and the instructor is no longer there like a coiled spring ready to jump in and provide additional safety - it is up to each individual to consolidate this experience, be aware of their own skills fade and be open to getting instructional assistance if there is a chance it has faded. Learning the skill is more about depth of time practising it than depth of time being taught it. Even pros get skills fade too!
I'm also sure that the position of the climbing wall was not that after one teaching session for ten minutes, he could be let loose in the future without consolidation experience. I am sure the position of the wall staff was that he should consolidate his skills. At the end of the day, you can take the horse to water, but cannot make it drink. If an individual thinks he is safe to belay after 10 minutes two months ago, the problem lies with that individual, not with the wall who trained him.