But Why Didn't They Pour All of New Hallway?

I'll be glad to answer that question.  In the new plans, there are some changes to that portion of the hallway.  It previously was home to six classrooms.  With the renovation, it will be home to eight classrooms, bathrooms, and a mechanical room.  The addition of a mechanical room and bathrooms requires plumbing.  The hallway has plumbing that leads to the sinks located in the classrooms.  The plumbers have finished the kitchen and can now work on the same process in the new hallway. 

This is the area closest to the end of the old hallway.  Trenches have been dug to lay PVC plumbing. 

The plumbing is awaiting inspection. 

The view is from the end of the old hallway.  The bathrooms and mechanical room will be to the right.