I remember reading a fic a while ago about Tony volunteering to teach a bunch of kids engineering. He would sneak off once a week or whenever he could and take Dummy with him. I think one of the challenges was to make a roller coaster model or something like that. Tony made them write up proposals and why they thought their design would work. I am pretty sure that there was a pairing but I can't remember who. I do remember that someone does discover his activities.
Thanks in advance for anyone who follow my vague recollection,
EDIT: Found! Thanks to Bugeyedmonster for the quick find!
Things Unseen (That Are Captured on Film) by scifigrl47
the kids, Lego Mindstorms and Dummy are seen in Chapter 2