For the most part, slots become available whenever a learner passes their test, but this isn't always the case. A learner might have a change in their college timetable, work rota or access to childcare - any such circumstances might lead to a lack of availability on my part if I'm unable to accommodate that change. It could be that a learner might decide, having tried manual lessons, that driving an automatic car would suit them better. Or maybe a learner might find themselves unable to continue paying for lessons. 

Hence, the waiting list is fairly fluid and however available slots present themselves, I simply go to my waiting list and see who can fill that slot i.e. starting at the top of the list, with who is available on that day and at that time. 

My advice is to get on as many waiting lists as you can, to increase your chances of starting lessons as soon as possible.