I built a K'nex roller coaster a few days ago with a little help from the kids. The best thing about this K'nex kit is that I bought it for $2 at a local thrift store. I love to shop thrift stores for cool things for me and the kids. It's hard for me to resist a good deal.
This roller coaster was a perfect addition to our unschooling life. Unschooling is a style of homeschooling that trusts learning happens all the time. Our family learns when we build K'nex roller coasters, building with legos, playing games, playing with friends, reading books, watching TV etc...
While we were building the roller coaster the kids compared K'nex parts from the roller coaster set with parts from older K'nex sets we have and watched how I was putting it together. My daughter said "Hey, you're using triangles that's the strongest shape."
The kids keep going into the playroom to explore and play with the roller coaster. It has been one of the best $2 I have spent. And what a bargain!