Are Applescripts Backwards Compatible?

Hi, let me start by saying I am not a programmer but I have some knowledge in the field and I recently bought a Mac so I'm totally unfamiliar with older systems.

Anyways, I have dabbled with AppleScript and was able to modify some existing code to create my own sorting method. Now, this works just fine on my machine but a friend of mine would like to use my script and it doesn't work for him. I created the script using the latest version of Snow Leopard but he is still running an older Mac with Tiger. If I create a script using Snow Leopard will it ever work on Tiger? Are there any significant changes made to the script editor or the way each OS compile things that I should be aware of?