Constraint recipe
A double-booking puts the same teacher in two lessons in the same period. The timetable cannot run that way. Open both lessons, check for duplicate import rows or a manual move into an occupied slot, then move or restaff one lesson. Check the new slot for room and class clashes before you save.
Key takeaways
- One teacher, two lessons, same period: invalid.
- Duplicate import rows and manual edits onto occupied slots are common causes.
- Part-time availability limits where the lesson can move.
- Fix the clash before tuning spread or gap preferences.
Why this blocks publication
A teacher cannot be in two places at once. This is a must-not-break rule in every serious timetable system.
The clash usually comes from a manual drag onto an occupied slot, a duplicated spreadsheet row, or two separate lessons in the period plan that both list the same teacher.
What to trace before you move a lesson
Follow both lessons back to the period plan or import source. Note the class, room, and whether the lesson should be team-taught.
If the teacher is part-time, check teacher availability before moving the lesson into a non-working day.
What to do next
- Open the two lessons that share the teacher and period.
- Search the source data for duplicate rows or copied assignments.
- Decide which assignment is wrong and whether one row should be deleted.
- Review part-time working days and unavailable periods.
- Move, restaff, or delete the incorrect assignment.
- Recheck room and class clashes in the new slot.
Common mistakes
- Treating a double-booking as a preference violation
- Moving the lesson without checking the receiving room and class
- Deleting one lesson when the real problem is a duplicated import row
In Smootables
Conflicts detected
The following conflicts will occur if you proceed:
Teacher J. Rivera is already scheduledWorkshop safety at 10:15–11:45
Smootables treats one teacher in two overlapping lessons as impossible. When you run Generate timetable, the solver keeps each teacher in one place at a time. Team-taught lessons still require every assigned teacher to be free for the whole period.
If you drag a lesson onto a slot where that teacher already teaches, Conflicts detected names the other class and time before the change saves. After generation, Teacher no-conflict in the analysis summary confirms the grid stayed clean on that run.
- Trace both lessons to their source placement before moving or restaffing.
- Remove duplicate import rows before blaming the generator.
Quick answers
Is a teacher double-booking ever acceptable?
No. If the same teacher is required in two places at once, the timetable is not valid.
What is the safest first fix?
Trace both lessons to source data, then remove the duplicate or move one lesson to a slot where teacher, room, and class are all free.