Your SchoolPrism .proj file looks strange because it contains an empty
StartupObject
tag:
<PropertyGroup>
<StartupObject>
</StartupObject>
</PropertyGroup>
I cannot test this right now but you could either try to set:
1) App.xaml in the start-up project option or
2) Remove the tag (as it should find the App.xaml by default) or
3) re-create the SchoolPrism project only this time making sure its based on a WPF Application template (you might have used a Winforms template?)