My daughter trained at 3, with nighttime pull-ups until 4 - easy peasy. My son, ugh. He was mostly trained by the time he started kindergarten, but there were still 2-3 accidents a month. I think he's solid on it now, at 6 - he hasn't had an accident in three months. At least while he was at daycare they handled any accidents, but I hated getting regular calls from school to come clean him up when he started kindergarten. And let me say that there is nothing worse than sitting stuck in the school pickup line imagining your child sitting around in his own waste while you try to get to the parking lot.