Can anyone offer some advice about guitar playing positions.

Most right handed beginners tend to start with the less formal position - guitar on right leg.

At what stage or level would you recommend a switch to the formal classical position - guitar on left leg.

Obviously age/arm length will be a factor in this, but do you know if examiners have any expectations that from a certain grade, the formal classical position should be adopted.

Thanks

In schools;

For children aged 9,10 and 11; I show them the proper classical position in the first lesson but do not use footstools as it is not likely that they have one a home. (Most will not even purchase a music stand!). Most children will prefer this postion, some will not but I remind them every week and in the end most will play with the guitar between their legs. I try to sit them on a chair or bench that is not too high. I teach most of them 'popular' guitar i.e. reading music and a full simple chords. It is unlikely that most of these children will take exams. If they show an interest, and aptitude, I go on to teach them 'proper' classical guitar;then they have to hold the guitar in the proper classical way with a footstool or a pile of books or old videos. (Hold them together with elastic bands). Exams are then a possibility.

Privately;
No choice. I have a number of different height chairs available and they have to hold the guitar in the proper way with their left leg on a footstool. I insist that they have a footstool at home.

I don't think that an examiner would make any comment about how the guitar is held. Some candidates may be disabled in some way which may prevent them from holding a guitar, or any instrument, in the traditional way.

I, personally, find it very difficult to have a good right-hand technique if I play with the guitar on my right leg.

The syllabus simply says "Candidates should provide themselves with a footstool and music stand if required". Most examiners know so little about the guitar that it is very unlikely they would comment on the absence of a footstool.
However, I really do believe it would be a great mistake to allow students to try for even Grade 1 who have not been used to 'proper' position, and whether they use a footstool, guitar rest or other device to achieve that is not really important. There is rather a divide among guitar teachers as to whether they automatically start beginners with proper position, and it may not be unfair to characterise the divide as being between 'serious' and 'less serious' tutors, the former going for the right position right from the start.
This has always been my approach and I have literally never had anyone have a real problem with it. I just say, 'Right this is how we sit to hold the guitar'...and that's it. Some girls take a while to get used to it, for their own reasons, but I'm not going to have them put behind the boys' progress because of that.
We do need to do what we can to make sure that pupils play with an appropriate position when practising at home, and while there are limits to what can be done to achieve this, I don't think the difficulty can possibly be an excuse for not having the student play properly in the lesson...its just a recipe for seriously flawed future technique.

I believe that to advance in your studies as a classical guitarist, a correct position is absolutely essential. If you allow students to develop a method of playing from any other position, it will at some point create problems as they advance.
Classical guitar, classical position.
That isn't to say that any other position is wrong.
To produce well grounded students, a tutor should be capable of teaching the methods you would adopt to play other styles.