I worked for a large school in London area and students had 2 options
1 - PAY FOR ALL GROUND AND FLIGHT TRAINING INC PRICE
2 - PAY FOR FLIGHT TRAINING ONLY AND GET BILLED FOR ANY GS USED
Worked well in that if they had paid for groundschool then they attended group scheduled student briefings
If they wanted to pay as they needed groundschool then they could do that
Either way I got paid for ground briefings and they tended to be done when not suitable for flying. These were lkey ong briefs such as NAV and CIRCUIT BRIEF.
The 20 min pre-flight brief was not charged however.