Personally, I preferred 2:1.
Basically, you’re paying for (e.g.) 4 half-days of driving practice. Now, you can either do that as 4 actual half-days, or you can do it as 4 whole days where you’re only driving for half the time. Is it better for you to spend the second half of each day at home/shopping/etc., or sitting watching the other learner? In my experience, I found it useful to sit and watch the other learner as I could also learn from his mistakes, and the advice the instructor was giving him.
Peter Smythe:
The easiest example is 2 folks on an artic. One cracks the reverse in 20 minutes (not that unusual) and the other one is no-where near after a couple of hours (also not unheard of). What does the trainer do? He either has to drag the second one off the area and go driving or he leaves him to practice and the one who’s cracked it is left kicking his heels. (And probably his arse wishing he’d booked 1:1!).
I’d say that’s quite simple. Let’s say that your client has paid for 14 hours’ worth of driving, and you typically allocate one hour per driver for reversing practice. If the “slow learner” needs more time to learn reversing, then it comes out of his/her’s driving time. You can either keep at it by extending the practice session (which means that you will need to shorten another one of that driver’s normal driving stints), or you can drag them off to go driving again, but come back to reversing for the “slow learner” by taking up some other time from that driver’s “normal” driving stints. They may benefit from having a break to do something different and then coming back to it fresh on a different day rather than getting agitated/despondent by continuing to fail. So, the “quick learner” would get 13 hours 40 minutes of “normal driving” but the slow learner gets 12 hours. How you arrange this time over the available training period is up to you. This is effectively what you would do if they were separate 1:1 sessions.
Basically, IMHO, 2:1 training should be operated as two separate 1:1 training sessions in terms of time allocation, just that the non-driving trainee is able to watch the other trainee’s driving.
To the OP: this is a debate that will run on and on (there are regular discussions on it on TNUK, and different people have different opinions). There is no one answer, as it is mostly down to personal preference.
Peter Smythe:
And I repeat that, although we only do this at weekends, 7 hour sessions 1:1 produce extremely good results (not a fail in living memory).
Not having a go, Pete, but could you clarify what you mean by that “not a fail in living memory” statement? I think the way that you categorise “fail” could be taken to be misleading. I think that many people would read that as being “everyone who took our 7-hour session training passed first-time”, whereas given another posting I’ve seen from you, I think it actually means “everyone who took our 7-hour training session eventually passed, but not all passed first time”. If it really is the former, then please accept my apologies 
