Is not so simple. When telling the computer you are looking for a certain flag, if its a student report it will only show the students of that flag, if its a parent list it will show any parent that has a child with that flag. The same is when querying for a period if you are looking at a students it will only show students of that criteria if you are looking on a parent list it will show you the parents of any child.
What you are trying to see is looking at a students but check if the parent meets the criteria. You can do this manually by editing the query in the edit tab. Just copy and paste from the 3rd box to the top box and click on update.