If nav planning, sometimes even in this day and age, some people don't have access to computers therefore have to finish the planning 'in the office'. I have no problem with this.
If a student isn't prepared for the nav lesson then I'll get them to plan while I engage in other things then when they've finished I ask them for the planned fligth time and fuel requirements. Then, innocently, ask them what time they've booked there lesson until. Square pegs / round holes. Doesn't happen that often now!