As your child with CP is becoming a teenager, there are a couple of things you may want to think about.
Spasticity is a condition of muscles that is a velocity resistance to stretch. What that means to a child and to a parent is that if you move the limb slowly, you have a difference than if you move that limb fast. Spasticity restricts movement and it creates a break on the system. It's as if they're trying to move, but they're held back. By treating spasticity, you may improve the range of motion or the action of the movement.
Upper limb therapies and interventions have been well studied in cerebral palsy. Different interventions that have good evidence are Constraint Induced Movement Therapy (CIMT) and Bimanual Therapy. CIMT has been shown to be successful in children with hemiplegic cerebral palsy (CP). CIMT uses a splint to physically constrain the uninvolved arm and encourage them to use the more involved or affected arm.