What Are Option Blocks? How to Build Them from Student Choices

Option blocks group elective subjects into sets that are timetabled at the same time, so each student can take only one subject per block. The main goal when building them is to let as many students as possible get their full combination of choices; fewer sections and balanced class sizes come second.

What an option block is

In the IB Diploma, students usually take 3 HL and 3 SL subjects; in A-Level, typically 3–4 subjects. A school cannot timetable every combination separately, so subjects are grouped into blocks. For example, Block A might run Physics, Economics and History together, and Block B Chemistry, Business and Literature.

All subjects in one block occupy exactly the same periods, so a student can attend at most one of them. A popular subject can run as several sections placed in different blocks.

What you are optimizing

A typical order of priorities:

• Full satisfaction first: maximize the number of students whose whole choice set fits;
• Sensible section count: with equal satisfaction, fewer sections save teachers and rooms;
• Balanced sizes: sections of the same subject should be close in size, not 30-plus in one and a dozen in another.

Constraints that must hold

• A teacher cannot teach two sections in the same block;
• The number of sections running in a block cannot exceed the rooms available, with labs and specialist rooms counted separately;
• Each section has a maximum class size;
• When year groups share one block grid (for example DP1 and DP2), teachers who teach both years must not clash.

Why doing it by hand in Excel hurts

The manual approach often takes weeks: sketch blocks from experience, then check every student to confirm they have at most one subject per block. Every time you move a subject, you have to recheck every student who chose it, plus teachers and rooms. With many subjects and students, it is hard to know whether you are anywhere near the best possible arrangement.

What to check in a result

• Full-satisfaction rate: how many students got every subject they chose;
• Clash list: for each unsatisfied student, which two subjects collide in the same block;
• Section sizes: sizes per subject and the gap between largest and smallest;
• Teacher load: lessons per teacher per block, and any clashes or overload.

For a worked example see the G9 IGCSE case, and for more on international schools see International schools.

How Keyi handles it

• Designs blocks from imported student choices: maximizes fully satisfied students first, then applies the school's chosen strategy (fewest sections, smaller classes or a target class size), with balance as the final tie-breaker;
• Treats teacher clashes, room counts and class-size caps as hard constraints, and supports one shared block grid across year groups;
• Shows every unsatisfied student with the exact reason;
• In an IB DP sample school (144 students, 33 teachers, 97 teaching groups), 138 students (95.8%) were fully satisfied and the first clash-free timetable was produced in 0.6 s.

Want to try it with your own students' choices? Book a demo.