DropDown -- SelectedIndexChanged

I am having trouble with SelectedIndexChanged event on my DropDown control on my WebForm.

I have a dropdown control, I want to run some code when the selection is changed, but cannot get the proper event or something. I set a breakpoint into the CourseDropDown_SelectedIndexChanged(object sender, System.EventArgs e) function, but it is not triggered or something.

How do I do this? Any help will be appreciated.

Keener