You see the same profile of difficulty among the educated Bostonian adults, and the going-to-school Bostonian kids, and the adults and children in the Amazon. The problems that were hard for them were hard for us.
A lot of children find symbolic arithmetic quite difficult and tedious, yet the children loved our tasks. They were games, the children were very happy to play them, and they were also they were good at them.
I think it's really fascinating that geometry is so difficult. My guess is it's difficult because it focuses on proofs.