Unit Blocks for All!
Sadly, this article highlights their use at private and charter schools. It suggests that blocks are the province of the public school, but that may only be true in New York and similarly funded states: here in California, if you don't have unit blocks in your classroom, there sure isn't room in your budget to buy them.
I have about a third of what the article says would outfit a classroom ($1,000 of blocks). The kids do get an incredible amount of collaborative concept development out of the blocks, including thinking about properties of physics, engineering and social studies (what buildings does a community need?, etc.). Sadly, what I don't really have are the arches and curves that the photo shows. I tried to get them off Donors Choose this year, but that project expired. Maybe I'll try again when I have an open slot.