The lifetime of an action learning program varies depending very much on the reasons for its formation in the first place and the success of the group in practice. Although sets can be formed for ‘one off’ occasions generally the idea is that once a set is formed members continue to meet and support each other over a period of time, say over several months. The real benefit of action learning sets comes being part of a mutually supportive group who can help each other work on their issues. If all members in a typical group of 6 or 7 are to be supported then it is likely that more than one session would be needed to ensure that all members receive the help they are looking for.
Part of the action learning process is the accountability to the group for actions agreed and by this definition a group would need to meet again for the issue holders of the previous session to report back on progress.
Also the skills required by members to effectively work together take time to develop and a group generally needs time to gel and get used to the action learning process.
Some successful action learning sets once formed continue to meet over a period of many years benefiting from the strong cohesion between members.