The school schedule is a weekly "classroom x day" chart: where and when course lessons and events take place. It is not a schedule of opening lessons within a course.
To open the school schedule, go to "Education" → "Dashboard" and click the "Schedule" tile (or go to "Reports" → "Class Schedule"). Use the arrows or the calendar to select a week. The cells contain reservations: clicking on a course lesson opens the reservations modal, and clicking on an event opens the event card.
The checkerboard is filled only after setting up audiences - first, create them in the "Audiences" section.