In order to determine if the checkbox is checked you can define properties in your business model and then define GridView's
columns like :
In the example, "Married" is of type bool, so the GridView will generate checkBox column by defaut. Then in selection_Changed event you can check the value of "Married" property is true or false. I would suggest you to work with the data objects instead of the visual elements.
In case that does not help you, please tell me what your exact scenario is.
the Telerik team