Of all the trials and tribulations facing parents, early success with potty-training is still considered the nirvana towards which we must all strive. There's more literature, advice and equipment devoted to this subject than almost any other - and yet it's the one that causes the most frustration. Most children aren't ready to begin toilet training until their second birthday. Before then, a child is more likely to play with the potty than sit on it. But, as with anything to do with development, every child is different. The key to success is to recognise when your child is ready - and to resist all efforts to start earlier just because some smug mother at toddler group announces her child no longer needs nappies. 'The most common mistake is to start too early,' says Dr Kathleen Reynolds, a general practitioner with Dr Anne Spooner & Associates. 'Some children will be ready at two years. But for others, three years is the norm. The point is: it doesn't matter.' A child is ready to start potty-training when he: Stays dry for a few hours each day; Takes an interest when someone else uses the toilet; Has bowel movements at regular times of the day; Can demonstrate when a bowel movement is taking place (such as by squatting); Lets you know he wants to be changed when his nappy is soiled. If you begin before your child is physically ready, you'll be asking something of him he's simply not mature enough to give, and there's bound to be stress. And if you press ahead before your child is emotionally ready, you're simply trying to impose your will on your child in an area where you can't win. Attempts to force the issue are an open invitation for the child to experience successful defiance. If a pre-school place is the issue, it's worth bearing in mind that, if the child is light years from being toilet trained, he might not be prepared for the more structured environment of nursery school, either. 'An early start means the learning process takes longer, at great emotional cost to both parent and child,' says Reynolds. 'If you start later, the child will learn faster and reach the same point at the same time.' The timing must be good for the parent, too. Potty-training requires dedication and the patience of a saint. If you're about to move house, are expecting a baby or experiencing major upheaval, don't even think about it. Above all, keep the issue in perspective. University entrance application forms don't demand to know at what age you started potty-training. Children are biologically motivated to learn this skill and they will ... when they're ready.