Along the same lines, once I finished Part 1 of Tactics, I didn't see the 'Continue Course' button, which is the only correct Call To Action above the fold. I thought I was done with Tactics, and went back to the main screen and tried the Diving Deep part. Please highlight that button better.

Other than that, this is a genius startup idea, really fun, and really addictive. I don't even intend to play chess very often and yet I'm addicted to picking up this skill now!