How can "small" small businesses most effectively map their business processes when they are in rapid growth mode?

Business Process Mapping refers to activities involved in defining exactly what a business entity does, who is responsible, to what standard a process should be completed and how the success of a business process can be determined. Once this is done, there can be no uncertainty as to the requirements of every internal business process.

I'm interested in ideas and suggestions on effective techniques for mapping business processes in small service businesses in growth mode where the BPM can become both something to improve upon as well as a training tool for replicating the business.