The iPad offers two position for the on-screen keyboard - Docked and Undocked.
By default, the iPad's on-screen keyboard is docked at the button of the screen, while undocked mode will shift the keyboard up to the middle of the screen.
To Dock your keyboard,
1. Tap and Hold the keyboard icon in the lower right corner of your keyboard
2. Move your finger to Dock option, and your keyboard should back to the bottom of the screen.