Are you able to attach dummy data and/or the view you are looking for?
Just a few ideas....
You could create two Measures - "inflow" and "outflow" at the School level.
You may also need to create two Dimensions - "inflow from" and "inflow to" - these would be school Ids to link to the "inflow" and "outflow" measures at the school level.
Then you should be able to show both at the same time.