Thank you for the help.My school Admins were assigned their roles from the Site administration / Users / Permissions / Assign system roles. (Because the roles had been defined in the above line "Define roles” option.)
I went back and selected Site administration / Courses / Add/edit courses, clicked on the Category for the 1st School, and then Settings / Assign roles.By assigning them to the same role, but under the school's Category limited their views to only that one school.Just what I wanted it to do.
I think that this might be useful to explain in more detail on future versions of MoodleDocs.Until then, I included the steps above for others that may have the same question.
Thanks again! J