Auto-Lock in iOS 9 when using Guided Access®
In iOS 9, the sleep function has changed when Guided Access® is enabled. In the default configuration, the Auto-Lock time is no longer used when Guided Access® is enabled. Instead, the device will remain active and drain the battery. However, there is a setting change that will improve this behavior. When the Sleep/Wake hardware button option is turned on, the device will sleep after a period of time. In addition, the device lock button can be pressed to lock the device immediately.
To turn the Sleep/Wake button option on, triple-click the Home button on your device. In the Guided Access® settings, Touch the Options button under Hardware Buttons and then switch the Sleep/Wake button to ON. You will need to do this for all apps that use Guided Access®