Ask anyone with twenty years in construction who taught them the most, and the answer usually arrives with a name and a story. Often it is not their line manager. It is the site manager who walked them round the job at seven in the morning, the senior QS who let them sit in on a final account meeting, or the foreman who explained why the drawing was wrong.

9 votes in so far, with the poll open until 5pm today. The room split like this: 44% said nobody, I worked it out myself, 33% said my line manager, 22% said someone on site: a foreman, a trade, a site manager.

Three things worth taking from that.

1. Learning in this industry happens beside the work, not above it. A line manager owns your development on paper, but most of what matters is picked up by being in the room when a decision is made: on site, in a valuation, on a difficult call with a client. Whoever takes you into those rooms is your teacher, whatever the org chart says.

2. The best teachers are rarely asked. A foreman with thirty years on the tools, a buyer who knows every subcontractor in the region, a planner who has watched a hundred programmes slip. Most of them would gladly pass it on, and almost nobody asks. That is the reason the Exchange exists.

3. Working it out yourself is the expensive route. Some people genuinely had nobody. They got there, but it took longer and cost more mistakes than it needed to. If that was you, you are exactly the person who should be teaching now.

If you are in your first five years, do not wait to be assigned a mentor. Pick the person on your job whose judgement you trust, ask to shadow them on one thing a week, and make it easy for them to say yes.

If you run a business, look at who your graduates and trainees actually spend their time with. If it is only their line manager and a training plan, they are missing most of what the industry has to teach them. Put them next to your best site people on purpose, and count that time as work rather than a favour.

So, my answer. The person who teaches you the most is the one who lets you watch them make decisions, and you usually have to go and find them. The Exchange is one way to do that: three things you could teach, three you want to learn, and half an hour with someone from a different generation.

The poll stays open until 5pm today. If someone taught you the job and never knew it, tell us in the replies who they were and what they taught you.