Option blocks: how to build them from student choices

Every spring, thousands of Year 9 and Year 11 students choose their GCSE or A level subjects. A few weeks later, someone has to turn those choices into a timetable. Option blocks are the traditional way to do it.

What an option block is

An option block is a set of subjects that are all taught at the same time. A student takes one subject from each block.

Suppose Year 10 students choose four subjects. You might build four blocks:

Block A	Block B	Block C	Block D
History	Geography	Computer science	Art
French	History	Business	Music
Triple science	Spanish	Geography	PE
Design technology	Drama	Food	Computer science

Every subject in Block A is taught in the same periods each week. A student who chooses history and geography takes history in Block A and geography in Block B. Popular subjects, like history, geography and computer science here, can appear in more than one block.

Blocks make the timetable simpler: instead of scheduling dozens of subjects separately, you schedule four blocks.

Step 1: Collect choices early

The earlier you have students' choices, the more time you have to build blocks that fit them. Many schools collect choices in the spring term so blocks are ready before the main timetable build.

Ask for a reserve choice as well. When a student's combination won't fit, a reserve gives you an agreed alternative instead of a difficult conversation in July.

Step 2: Decide what's fixed

Before you build blocks, settle the constraints:

How many blocks, and how many periods a week each one gets
Maximum class size for each subject
How many groups you can staff for each subject, given your teachers
Specialist rooms: three practical science groups at once need three labs at once
Subjects that can't share a block, for example because the same teacher teaches both

Step 3: Build the blocks from the choices

The aim is to place subjects in blocks so that as many students as possible get every subject they chose. A sensible order:

Count the demand. How many students chose each subject, and how many groups does that need?
Find the common pairs. Subjects often chosen together must go in different blocks. If 60 students chose both history and geography, they can't share a block.
Place the big subjects first. Subjects that need several groups are the hardest to fit, so give them blocks first and spread their groups across blocks where possible.
Fill in the rest, checking each placement against the common pairs.
Check every student. Count how many students get all their choices, and list those who don't.

Step 4: Deal with students who don't fit

There's almost always a handful of students whose combination doesn't fit. You can:

Move a subject to a different block, if it doesn't break someone else's combination
Offer the student their reserve choice
Add an extra group of a subject in another block, if you can staff it
Accept a clash for a very small number and arrange alternative provision

Keep a record of which students didn't get their first choices and why. You'll need it when parents ask.

Step 5: Test before you commit

Once the blocks are set, they constrain the rest of the timetable. Before you commit, check that the blocks can be staffed alongside the other year groups. A Year 10 block that needs four science teachers at once can collide with Year 11 setting. Timetable the blocks for several year groups together rather than one at a time.

Timetabling without fixed blocks

Option blocks exist because building a timetable around every student's individual choices used to be impractical by hand. The cost is that some students don't get the combination they wanted, simply because two of their subjects ended up in the same block.

The alternative is to schedule each subject's groups individually and check every student's choices for clashes directly. By hand, that's close to impossible for a full year group. For software, it's routine: the clash check for each student is exactly the kind of work a computer does well.

Timez works this way. It takes each student's enrolments and builds a timetable where no student is ever in two lessons at once, without needing blocks. You can still keep blocks if your curriculum relies on them, but you don't have to design them by hand first.

Quick checklist

Choices collected, with reserves
Group sizes and staffing agreed for each subject
Common subject pairs identified
Blocks built, and the number of students with all choices counted
Students who don't fit listed, with a plan for each
Blocks tested against the rest of the timetable

Next: see how option blocks fit into the full timetabling process.