One on one is definitely the most effective option, for beginner Skiers or Snowboarders it allows you to develop at your own speed, for intermediates it allows you to concentrate on specific topics to better your all round riding. For advanced, you can choose a topic and spend as much time as necessary to perfect your ability under the watchful eyes of one of our trainers.
An alternative would be to book one Instructor or Trainer for the whole family, taking it in turns this allows one member of the family to practice what they have learned whilst another takes instruction, swapping periodically.