I have no idea - my DS is just 2 and starting to take an interest in the toilet, actually also starting to realise when he's done a poo in his nappy, not that he'll come and tell me yet but if i ask he'll reply "poo" and point to the nappy so we're makign very tiny amounts of progress, no idea about standing or sitting, occassionally when he's int eh shower he'll pee and thinks it's hillarious but that doesn't really help does it! Anyone else???

My son learnt standing.. but he had his dad helping him out..  and he also learnt to go outside more than in the bathroom (the country life!!)..  my friend who is a single mum is asking a similar question  as her son only ever sees them sitting..  i dont really think it matters too much in the early stages, and once they get the hang of it, teach them to stand..   

but i wonder if it would pose any problems later on if they tend to prefer to sit.. like when they go off to school and all the others boys stand.. i dont really know, but something to think about i suppose??

And just adding to what Chugga has said about skills and coordination.. You still need to be careful when they sit.. you may need to teach them to push it down so they aim into the bowl.. when my nephew was learning we found that if he didnt push it down a bit he would spray all over the room!!