I\'m setting up some demo code for a beginner session on accessibility and I found that I am able to access an internal protected property from a derived class. What am I missin
Because it's how internal protected is intended to work. Access is given for either children in inheritance tree (protected part) or for the same assembly (internal part) - see Access Modifiers on MSDN.
And your ExampleClass is in the inheritance tree of BaseClass, which defines Prop5. So the access is thanks to protected part.