On "help me do it myself" puzzles

I should start writing what L. does, or these moments will belong to a continuous of time I won't be able to single out when I'll look back.

I'll start with puzzles.
I introduced puzzles gradually.
I started too early with a 3-circle puzzle. He must have been 12 months, more or less. He wasn't able to finish it and would just get frustrated.

L. spends very little time at home with his toys, and while his gross motor skills benefit *a lot* from daycare, quiet activities like stacking, matching, puzzling (..) are left on the side. At around 15 months I offered again the 3-circle puzzle and was a hit.
I also took a video that would be a perfect Montessori spot, all about self-correction and repetition.

At around 16 months I introduced more circles, but it was too easy. So I went with single more complicated shapes. Square and triangle, first separately then together.

It worked.
By 19 months I wanted to scale it up a bit.
I offered again square and triangle that were out for rotation. He took some times to get that again, but now he passes by the shelf and fits them in, casually, between a tour on his little bike and a climbing adventure on the couch. I don't even notice him doing it most of the time, I just find the puzzle completed.
I'll leave them out as long as I find that he's using it.
And I offered this as well:

I like it, because he's guided by the image on the board, and because the knob are
I wasn't sure he would pick it up. He's in love with transportation now (and ambulances firetrucks dumpers diggers bulldozer), so I figured that the single pieces would meet his interested even if the puzzle was too hard.
I planned to offer some matching activities first, but I didn't find the time to make it, and now that I did, he doesn't seem to care.

It turned out it wasn't necessary. This morning (19.5m) he completed the puzzle by himself. Almost by himself, because he asked for help when I sat besides him, although there was only a piece missing.

Two beautiful links on toddler and puzzles:
12-18 months
18-24 months

Also, notice the way the puzzle is offered. Dismantled. It makes a key difference. And it helps for clean-up as well.