There is no need to have the layout grid containing Commit time and Evaluation time positioned inside the Student-Dataview. Check what happens if you copy the to outside the Student-Dataview. The dates will probably show up.
And just to know what is going on, add Column1 and Column2 as well to the SampleVisibility-Dataview.
Something else: the Student-Datagrid that you retrieve from database is oddly placed inside the SampleVisibility-Dataview. I would expect it outside the SampleVisibility-Dataview since the two are not related.