The school timetable is one of the most complex documents a school produces, and one of the most fragile. Change one teacher's period and three others shift. Most timetables are built by one experienced person over several days — and when that person is away, nobody else knows how it fits together.

Start with the constraints, in order

A timetable is a set of rules. Write them down before placing a single period. List them from hardest to softest:

Hard constraints — must never be broken: a teacher can't be in two places at once; a class can't have two subjects at once; a lab can only host one class.
Required counts — each subject needs a set number of periods per week for each class.
Teacher limits — maximum periods per day and per week, and any part-time availability.
Soft preferences — maths in the morning, no double free periods, PE not right after lunch.

Step-by-step method

Step 1: Set the bell schedule

Define periods, breaks and assembly for each day, including any shorter days. Everything else hangs off this grid.

Step 2: Place the most constrained items first

Labs, shared specialist teachers, and part-time staff have the fewest options. Place them first, while the grid is empty. Leaving them to the end is the most common reason timetables don't fit.

Step 3: Fill core subjects

Place daily subjects — languages, maths, science — spreading each across the week rather than clustering them.

Step 4: Fill the rest and balance load

Add remaining subjects, then check each teacher's daily load. Look for anyone with six periods on Monday and two on Friday, and rebalance.

Step 5: Check for clashes — automatically if you can

On paper, clash-checking means scanning every teacher's row by eye. In software, clashes are flagged the moment you create one.

Plan for substitutions

Teachers are absent. A timetable that shows who's free in each period makes arranging substitutes a two-minute job instead of a morning scramble. When leave is approved in the same system, the gaps show up automatically — see staff payroll and leave management.

Share it properly

A timetable printed on the staff room wall is out of date the first time it changes. Publish it digitally so teachers see their own schedule on their phone, and students and parents see the class timetable in their app.

Reuse, don't rebuild

Most of next year's timetable looks like this year's. Starting from last year's version and adjusting for staffing changes is far faster than starting from blank. Export and import also make it easy to share drafts for review.

How Schoolo helps

Schoolo's timetable module supports weekly schedules, bell timings, and import/export, and it ties into attendance and the class diary so each period links to the right teacher and subject. If you're thinking about where else teachers lose time, read where teachers' time really goes and our guide to the digital homework and class diary.