Changing a timetable mid-year without breaking everything

The short answer: changing a timetable in the middle of the year starts with locking, not with calculating. You lock what works, change only what must change, and recalculate so that as few lessons as possible move. Then you compare with the previous version, and show each teacher exactly what changed for her. You build a timetable from zero only when the change is really big.

The reason is simple: in the middle of the year teachers and students already have a routine. A new timetable that is "better" on paper but moves half the lessons creates more mess than it solves.

First: is this a timetable change at all?

Not every change justifies a new timetable. An absence of a few days or weeks is a matter of substitutions. A timetable change suits when something permanent has changed: a teacher left, a new teacher arrived, the number of hours of a subject changed, or there is a new permanent constraint.

Common cases and what to do in each

A teacher left

1. You move the teacher to the archive in the teachers list. She is not deleted, and the constraints she submitted are kept. The links sent to her stop working.
2. In the classes and subjects table, for each of her lessons you set another teacher, or leave "System chooses" so that the solver chooses from the qualified teachers.
3. You lock and recalculate (see below).

A new teacher arrived

1. You add her with subjects, grades and maximum periods a day.
2. You send her a constraint request by link, and approve what she submitted. Details in the guide to teacher constraints.
3. You place her in lessons in the classes table, or leave it to the system to choose.
4. You lock and recalculate.

The hours of a subject changed

You change the number of weekly hours in the classes table. An hour that was added needs room, and an hour that was removed frees room. Here too: lock what must stay, and recalculate.

Locking and recalculating with minimum changes

This is the heart of a mid-year change. In Teaching School it looks like this:

1. You open the published version in the timetable board.
2. You press a lesson and choose "Lock" for everything that must stay in place. For example lessons tied to the hour of a hall or of a shared teacher. You can also drag a lesson to another cell, and it locks in the new place.
3. You press "Solve again". The solver sees the whole school, but "pays" for every lesson that moves from the previous version. That is why it changes as little as possible.
4. A new version is created, marked "After a manual change". The published version was not touched.

A made-up example: an English teacher in the middle school left, and her 8 periods move to another teacher who already teaches periods in the grade. You lock the physical education lessons (one hall) and recalculate. The solver will try to move only the English lessons in which the teacher who received them is already busy, and what has to move to free room for them. Exactly how much will move depends on the school, and you check that by comparing versions before you publish.

If the change is very big, for example a change of teaching days, there is also "Solve a new one from scratch". That is no longer minimum changes, and it should be used with care. Note that if you change the school week, constraints that no longer fit it return for checking.

And if there is no timetable that meets all the mandatory ones, you get the rules that contradict each other, and so you know what to release. A locked lesson can also be one of them.

When to make the change

A change in the middle of the week confuses everyone. A few simple rules:

• A change takes effect from the start of a week, and not in the middle of one.
• Send the proposal a few days ahead, so that teachers have time to respond.
• Until the change takes effect, handle the gaps with substitutions. A teacher who left on Tuesday does not require a new timetable on Wednesday.
• Tell the classes too. Teachers will receive their timetable, but students and parents need to hear about the change from the school.

Comparing versions and sending to the teachers

Before you publish, you check what changed. On the board there is "Mark what changed compared with version N", which shows how many cells changed and marks them. This is the moment to ask: is the change reasonable? Did one class get too much of a shake-up?

Then "Send to teachers". The proposal is sent to all the teachers who have lessons in the version, and each teacher sees only her own timetable. The proposal says how many of her lessons changed compared with the published timetable, and every lesson that changed is marked "changed". A teacher for whom nothing changed sees that at once. Whoever has a comment writes it, and the comment becomes a constraint waiting for your approval. After you approve, you can "Solve again from the feedback".

"Publish" turns the new version into the active timetable. The previous version moves to the archive, and you can download any version from the archive as an Excel file.

The whole process, from setup to publishing, is in the complete guide to building a timetable. And if you are choosing a tool and want to know what to check about corrections, see 8 questions before you choose timetable software.

Written by the Teaching team · Updated on 14 October 2026.