Determining the absolute oldest school in North Dakota is difficult due to the evolution of schools and the lack of complete historical records for all early educational institutions. However,
the Pembina County Agricultural School (which later became part of the University of North Dakota system) is often cited as one of the earliest, if not *the* earliest, formal schools in the territory that eventually became North Dakota. It was established in the 1880s.
It's important to note that there were likely earlier informal schools or teaching initiatives in various settlements, but the Pembina County Agricultural School represents one of the first formalized and relatively well-documented educational institutions in the area.