I tried with dd3, didn't want to know, left it 6 months, still didn't want to know. So I left it again. The HV said just forget about it - she'll do it when she's ready.
She is 3 years, 4 months old. Yesterday morning she woke up and said 'I don't like wet nappies', took her nappy off and has been weeing in potty by herself ever since. Now, this many not be the end of any problems I know. But my point is that I don't think there is any point doing 'training' until they decide they are emotionally ready. Dd3 has understood for a very long time that big girls do wees in the potty / toilet etc but no amount of me sitting her on there or using reinforcers made her do it until she made the decision.