DS decided to spent saved allowance on Perplexus Epic. It is well beyond him, and I can get a bit further but the diminishing returns is frustrating as are the limited sightlines (make a mistake, start over to get to the point where you can work to master that bit.)
We looked at the Twist one yesterday and he had renewed interest in that one.
For building, I think K'Nex is a great way to go because it requires a decent engineering sense to make sure structures will support, that connectios are exposed in the right place for assembly, and many use motors and the finished products (e.g. roller coaster) are fun as built. I had some years ago for my own amusement and DS got the rollercoaster a couple of christmases ago, I ended up building it as he learned to read the manual and get the parts and coach me in my assembly.
e.g.
http://www.target.com/p/knex-space-...905785#prodSlot=dlp_medium_1_3&term=knex
