At some point in your instructing career you will have to answer the question "is my student ready to drive solo?". A related question is "is my student ready to move up to the next group?", but this is a topic for another essay. Today I will talk about my thought process with respect to soloing students.
Safety Vs Skills
Some track day promoters require instructors only for safety reasons. In other words, promoters only insist that drivers who are solo are safe to be solo, but not that such drivers have particular driving skills or pace.
Other promoters define expected driving skills for each run group, and an instructor is meant to teach these driving skills. In such organizations an instructor is expected to stay with their student until the student demonstrates that they have the required run group skills.
Safety And Minimum Requirements
My minimum requirements for solo drivers are outlined in Novice Solo promotion requirements. These mainly involve blend line, hand signals, knowing and observing flags and being aware of other cars on track.
Most People Are Sensible
While there are certainly exceptions, most people tend to not intentionally wreck, drive off track, drive erratically, etc. From running track days with promoters that require safety only for soloing, I've seen plenty of drivers who were well behaved despite having very little time on the track. Often times any incorrect behavior such drivers have is simply a result of them not knowing the right thing, and a gentle talk is all that is needed to set them on the right course.
Some organizations have specific skill requirements for each run group, and a solo driver in that run group is expected to have said skills.
As an instructor you should be aware of what these requirements are, and you should stay with your student until the student fulfills the requirements. It is handy to have a printed out checklist that you can go through with your student. I have a general skills checklist here.
This however does not mean that I will be working on only these requirements until the student masters them. Following the "Safety, Fun, Learning" principle, I will try to make sure the student is having fun while they are learning the required skills. As this is going on I will generally stay with the student.
This Track Vs Other Tracks
Especially upper novices and lower intermediate drivers may have several days of experience on a single track but they have not driven any other tracks. Such drivers may memorize the layout of the track they are familiar with but could be lost on a new track. It is often acceptable to solo a driver on a given track only but recommend that they get an instructor when they go to a new track.