You're a Divemaster. You've been thinking about the Instructor step for six months, maybe a year. You've opened four PADI IDC websites this week. Three of them don't mention group size anywhere.
There's a reason for that. And it's not a reason that serves you.
The numbers most dive centres don't want you to see
The PADI Instructor Development Course runs twelve to fourteen days. In that time, you need to master:
- Five to seven formal academic presentations, each evaluated individually
- Multiple confined-water teaching scenarios, each with a different role (instructor, assistant, student)
- Open-water teaching sessions in varying conditions
- The full PADI standards library
- Dive theory across five subject areas, tested in depth
A Course Director evaluating this work in a group of twenty candidates has roughly the same total hours as one evaluating eight. Do the math: each candidate gets less than half the individual attention.
This isn't a marketing claim. It's arithmetic.
Why four is the floor, not the ceiling
Most group-size conversations focus on the upper limit. The lower limit matters just as much.
PADI group teaching scenarios — a core part of the IDC curriculum — require a specific structure: one instructor candidate, one assistant candidate, and at least two student candidates. Below four participants, these exercises break down. Candidates can't rotate roles properly. Peer learning, which makes up half the real value of an IDC, disappears.
So the minimum defensible IDC group size is four.
What about the maximum? That's where the industry pretends the math doesn't exist.
The attention ceiling
A good Course Director can hold detailed, personalised feedback for each candidate in their head — presentation patterns, weak spots, teaching voice, language quirks, stress responses, trajectory. This is cognitive work, and it has a limit.
In my experience, that limit sits around eight.
At five or six candidates — which is what most of my IDCs actually look like — I can give each candidate feedback that's specific to their development curve, not generic standards-based feedback. I know whose nerves affect their briefings and whose don't. I know who needs to be pushed harder and who needs slack. I know who'll make an outstanding instructor and who's in the programme for reasons they haven't quite articulated to themselves.
At twelve, I start losing track of nuances. At twenty, I'm running a production line. And you — the candidate — become a throughput metric.
"A large IDC can produce candidates who pass the IE. A small IDC produces candidates who become instructors."
— Dominik Weckherlin
What "passing the IE" actually measures
Most IDC marketing leads with pass rates. "95% of our candidates pass the Instructor Examination!"
Here's what that number actually tells you: how well the programme prepares candidates to pass a specific exam. What it doesn't tell you is:
- Whether you'll be a confident instructor six months later
- Whether you'll still be teaching two years later
- Whether you'll have the judgment to handle edge cases — a panicking student, a borderline medical situation, a gear failure at depth
- Whether your teaching voice is yours, or a copy of your Course Director's
A large IDC can produce candidates who pass the IE. A small IDC produces candidates who become instructors.
The difference shows up later. By then, the dive centre that sold you the IDC has your money.
What to ask before you commit
If you're comparing IDCs, here are the questions that actually matter:
- How many candidates will be in my group? Accept a specific number, not a range like "up to 15." If they won't commit, assume the worst case.
- Who will be my Course Director — and will it be the same person for the whole IDC? Some centres rotate Course Directors or hand off portions to Staff Instructors. That changes the experience materially.
- What language will the course be taught in? If your first language isn't English, ask specifically whether the academic content (dive physics, physiology) will be available in a language you think fluently in. Translation during presentations is not the same as instruction in your own language.
- What happens if I need more time on a specific skill? A rigid schedule designed for a large group has no slack. A flexible schedule designed for a small group does.
- What's the plan if I don't pass a component on the first attempt? Every serious Course Director has an answer to this. If they don't, walk away.
- Can you introduce me to former candidates I can talk to? Names, not testimonials. Real people. If they can't provide any, that tells you something.
For partners, family, and other decision-makers
If you're reading this because someone you care about is considering the PADI Instructor step, here's what you need to understand:
Becoming a diving instructor is a career decision, not a hobby upgrade. It affects income, location, long-term physical demands, and identity. The quality of the Instructor Development Course shapes the quality of the career that follows.
A cheap IDC in a large group may save two to three thousand Swiss francs or euros up front. What it often costs: a candidate who passes the exam but lacks confidence in real teaching situations, burns out within a year, and either returns to the Divemaster role or leaves diving entirely.
A well-run small-group IDC costs more because it has to — the math of Course Director time per candidate is inescapable. What you're paying for isn't the certification card. It's the probability that your partner, son, daughter, or friend is actually prepared to do the job.
The right question isn't "where's the best deal?" It's "where will they come out as a real instructor?"
The honest conclusion
Group size is not a soft preference or a marketing differentiator. It's the single variable that most directly determines how well you'll be taught — and how well you'll teach afterwards.
Four to eight candidates. Usually five or six. Never more.
If you're looking at an IDC offer right now and the group size isn't stated clearly, ask. If the answer is vague or above eight, ask what they'll do with the extra spots.
A good Course Director leaves them empty on purpose.
This post is part of an ongoing series on what makes a PADI Instructor Development Course actually work. Related reading: What to expect during your IDC · From hobby diver to instructor · Why small groups make the difference