I started out using my parents old nitrocellulose T-Square and triangles when I was 11. I still used a T-Square for my summer at RISD, but once I started grad school, it was parallel rules from then on, except you needed the T-Square for constructing perspectives.
In the tribute page to a picnic shelter my dad did on NewHavenModern.org, I contributed a bunch of materials included pictures of both my parents at their drafting boards as well as a couple drawings. Having a tetrahedron for a roof, he was decidedly not drawing a square building in this case with that T-Square. I’ve contemplated making a model of it in SketchUp, but I don’t know when I’ll have the time to spare.