I believe the easiest way to pass values from/to a user control loaded within a page, is by creating a custom property of the user control, and setting/getting its value. For your convenience I implemented this approach, and attached the application to the thread. There are three buttons. One sets the value from the user control, and the other one from the page. The third displays the current value in the property.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.