As its used for tuition purposes, sometimes it does 60 miles in an hour, sometimes only 4 miles an hour if we are doing manoeuvres, as a guide I usually leave home at 8.30, start work at 10am, finish my last lesson at 7pm, and I am back home around 8pm. At that point the car has been running for 11.5 hours almost constantly, covered around 300 miles, and used approx £40 in fuel, or 30 (ish) litres, or 6.5 gallons, which equates to 46mpg as you say, however I prefer to think of it as 0.6 gallons per hour, or £3.60 per hour.
As a driving instructor we will never match the manufacturers mpg, however can you imagine what the mpg is when using a petrol Focus where the manufacturer claims 32mpg, realistically that would be around 24mpg as a tuition car. Thats why you need to start with a frugal car in the first place