Some children will respond in a short period (e.g. 12 sessions). However, much more time is required when problems are complicated or have persisted for a long time. Play Therapy often tries to help a child master complex emotional skills that they may have missed out on. It is similar to learning a language. If you learn it from birth it comes quite naturally, if you have to learn it later on it takes time to grasp fluently. In these circumstances, it is not unusual to work with a child for two years or more. Not because they are terribly disturbed but because the task is naturally time-consuming.