I have just completed the my 2015 edition of portrait painting. This year we had 14 students and eight models.
Students worked from a combination of life and photographs to incorporate the best of both in one painting. Essentially students used the photo for the drawing stage and the model to check colours and values. The goal was to make an interesting painting and so students worked within a traditional system used by master artists. A variety of examples of systems were explained and shared and students choose one they liked.
As part of the instruction I painted a demo from life explaining my process along the way:
Block-in with umber after 30 minutes
Completed painting 8 hours