CAS is part of the IB core, alongside the extended essay and theory of knowledge. It carries no points and it can still stop a diploma.
What it asks for
Engagement across three strands: creativity, physical activity, and service to others. Plus a longer CAS project undertaken with others over an extended period.
The programme is built around learning outcomes rather than a fixed number of hours, and the way a school implements it varies.
Reflections are the substance
What is submitted is not a list of what was done. It is reflection: what was attempted, what went wrong, what changed, what was learned.
A short honest account of a difficulty is worth more than a long description of a successful event. Reflections written in one sitting at the end of the two years read exactly like what they are.
The common failure
Leaving CAS until the final months. It cannot be compressed, because the requirement is engagement over time and the evidence carries dates.
Students in this position end up doing CAS during the same weeks as final revision and internal assessment deadlines, which is the worst possible arrangement.
The CAS project
Collaborative and sustained. It is meant to involve planning, working with others, encountering a problem and dealing with it.
A project that ran smoothly from start to finish usually produces weak reflections, because nothing was learned that could not have been predicted.
Why it matters despite carrying no points
An incomplete core is one of the conditions that prevents the diploma being awarded, regardless of subject grades. A student can pass every exam and still not receive the diploma.
That is the whole reason to keep the core visible on the calendar from the first term.