Almost always the reason an iPad will not charge at all or will not charge fully is due to using a faulty or incorrect charger.
Every student was issued with new iPad charger and cable when they were issued their iPad. If a charger or cable fails or is damaged it is the student's responsibility to replace it. We recommend using the correct charger (at least 12W) and cable from the Apple Store.
Cell phone chargers, including iPhone chargers and many 3rd party chargers do not supply enough power to fully charge an iPad.