Individuals with childhood-onset physical and developmental disabilities often have special needs around exercise and physical activity. However, most books on this topic are written for exercise science experts who may not always be the frontline service provider. The aim of this practical guide is to enable clinicians, and others involved in the provision of rehabilitation services to train and foster physical activity and physical fitness across the lifespan. It includes chapters on the principles of fitness testing and training, how to engage safely in physical activity, how to measure physical activity levels tracking progress and what to do if pain arises. It includes disorder-specific chapters that apply the general principles of physical activity training to specific diagnoses including autism, traumatic brain injury and juvenile arthritis.