After the trainee has completed the exercise with guidance from the instructor, all subsequent efforts should be conducted with the instructor remaining almost silent. Trainees should be advised, in advance, that the instructor will not be helping but will be watching for errors and will also intervene in the event of an emergency.
As before, the instructor should carefully observe and as soon as the trainees make errors, should intervene trying to encourage them to work out the faults themselves.
Apart from correcting faults the instructor should basically keep quiet and let the trainee(s) concentrate on doing the exercise. Depending upon the trainee(s) and their ability the exercise may need to be repeated several times.