After you qualify as a Rescue diver you can opt to turn pro. The first rung on this ladder is Dive Master. It's takes ten day's of intensive learning in the classroom, pool and sea. There is a great deal of emphasis on dive planning and supervision of both divers and students. As this is the first step towards becoming an instructor you are also introduced to some of the demands of that job.
Most dive masters go on to a working internship, to polish their skills.
From DM you can go to an Assistant Instructor and then on to an Instructor Development Course which will prepare you for your Instructor Examination. Varies according to options chosen, but usually around ten days, which can be followed by a period of internship.