This paper explores issues involved in scheduling teaching in a higher education institution. The goal is to provide a theoretical framework in which to understand why problems occur while generating teaching timetables. The paper proposes three likely effects of rules: One, that rules interact with other rules to produce greater rigidity than individual rules would appear to do alone. Two, that changes to the timetable cause greater disruption the more rigid the timetable has become. Three, there is a threshold point at which the rules set will prohibit the creation of any workable timetable for the required teaching using the available room and staff resource. The recommendation of this paper is for institutes of higher education to articulate and study their existing rules, as well as their 'expectations' that guide the creation of their yearly timetables.