The room and the first project

The temptation is to open with something that shows off the space. Resist it. A first session where everybody leaves holding a thing that works is worth more than any demonstration you could run.

Finishable beats impressive

Pick a project that the slowest attendee finishes inside 90 minutes, including the twenty minutes lost to arriving, chatting, and finding a seat. In practice that means something far smaller than you think: a line-following chassis with the code already written, a servo that responds to a distance sensor, a light that answers a button.

The mechanism you are building is not skill transfer — it is the feeling of having finished. People who finish come back. People who leave with a half-built thing in a bag do not, and the half-built thing is a small permanent reproach that makes returning harder rather than easier.

Before anybody else is in the room

You are now responsible for people who did not choose the kit, do not know the tools, and may be children.

Write the run book

Write the session as if you will not be there. Timings for each segment, the full kit list with quantities and spares, the three places people will get stuck, and the exact thing to say at each.

Then do the honest test: hand it to somebody who knows less than you and ask them what they would do at minute forty. Every question they ask is a hole.

Dry-run it on one person

Before advertising anything, run the whole session for a single friend who is not technical. Time each segment against your run book.

You are looking for one number: how long the slowest realistic person takes. If it is over 90 minutes, cut scope now rather than discovering it in front of twelve people.

Dry-run completion time

Minutes for your non-technical volunteer to finish, unaided. This sets the scope of session one.