Constraint recipe
If a part-time teacher does not work on Wednesdays, Wednesday is unavailable for every lesson that needs them. The harder question is whether their assigned periods fit into the remaining days without breaking team teaching, room rules, or pro-rated hour limits. Schools that trialled flexible working have reported part-time shares from 10 to 43 percent of staff, and too many staff off on the same day can make a timetable impossible.
Key takeaways
- Non-working days are unavailable for every lesson needing that teacher.
- Legal weekly hours can still be impossible to place in too few days.
- Team-taught lessons need a day that works for every teacher on them.
- Clustered days off can remove a whole weekday's capacity across the school.
Fixed days shrink the placement set
A 0.6 teacher working Monday, Tuesday, and Thursday has no valid slots on Wednesday or Friday. Every class needing that teacher competes for time on only three days, and labs, workshops, team teaching, and shared rooms may force those periods into even fewer windows.
Part-time contracts are also a school-wide pattern, not just an individual one. When many staff want the same day off, that weekday loses teaching capacity for everyone, which is why clustered non-working days are a known cause of impossible timetables.
A worked example: a 0.6 contract on three days
Ms. Niemi works Monday, Tuesday, and Thursday: 18 periods of possible time. She is assigned 12 lessons, which fits on paper. One of them is a team-taught lesson with Mr. Salo, and his non-working day is Thursday.
12 lessons in 18 possible periods
| Mon | Tue | Wed | Thu | Fri | |
|---|---|---|---|---|---|
| P1 | 7A | 7A | Off | 9A | Off |
| P2 | 7B | 8A | Off | 7A | Off |
| P3 | 9B team | Off | 8A | Off | |
| P4 | 8A | 7B | Off | 7B | Off |
| P5 | 9A | Off | Off | ||
| P6 | Off | Off |
- Lesson
- Team-taught lesson
- Non-working day
The lesson count was never the problem. Twelve lessons fit easily in eighteen periods, but the one shared lesson has a two-day window before any room or class check even starts. Compare assigned periods with pro-rated caps where your local rules require them, then check every shared lesson for a common working day. Start with part-time teacher workload if hour limits are part of your collective agreement.
Verify the days before you move lessons
- Record each part-time teacher's working and non-working days in the master data, and mark non-working days as unavailable, not as preferences.
- Sum assigned periods per teacher and compare with pro-rated caps if your agreement uses them.
- For team-taught and shared classes, list the days on which every required teacher works.
- Count how many part-time staff are off on each weekday; a day where many are off has less capacity for every class.
- If lessons do not fit, move load or change staffing. Treat a real non-working day as fixed.
Common part-time planning mistakes
- Checking weekly totals but not whether the periods fit on working days only
- Giving linked teachers different fixed days without testing their shared lessons
- Taking away a teacher's day off when the real issue is too many assigned lessons
In Smootables
Model a fixed non-working day as a repeating availability rule: open Resources, choose In-day time settings (repeating weekly), and block the whole weekday for that teacher. The generator then treats every slot on that day as off limits, exactly like any other unavailable period. One-off absences go under Dates when unavailable (full day) instead.
Each teacher also carries a Weekly max hours value. If assigned lessons exceed it, the period screen lists it under Validation Errors before generation runs, with the assigned and maximum hours side by side, so a part-time overload is caught as arithmetic before a generation run fails.
- Block the non-working weekday with a repeating rule, not by deleting lessons.
- Set Weekly max hours to the pro-rated contract value so the validation check reflects the real limit.
Quick answers
Can fixed part-time days make a timetable impossible?
Yes. If required lessons cannot fit on the teacher's working days, no generator can place them legally. Clustered days off across many staff make it worse.
What is the best first fix?
Recheck assignments and shared lessons. Move load or change staffing before weakening a true non-working day.