How can I create a toggle button template that will "slide" down when activated?

Question

WPF

Good morning!
I created a button template based on a copy: pastebin.com/KXbT4B3H
The task is this: to make the button move downwards when switching to the "Cheked" state. Tried being able to animate the "Height" property of the Grid element, but it didn't work.
Important: App for Windows 8 platform(WinRT)
Thank you all in advance for your help!