The following articles describes the Reordering feature of the RadGantt
You can reorder the tasks in the RadGantt by dragging the task rows within the Treelist area of the control. There are three possibilities when reordering certain task:
Drop above certain task
Drop bellow certain task
Drop over certain task and make it a child task.
If the task which is about to be reordered has child task, the hierarchy is persisted and child task is dragged along with its parent.