Academic motivation is virtually nonexistent in the States, whereas in China kids go to school on Saturdays and go to private cram schools until nighttime. A nation is made or broken by its education systems since after all, knowledge is power.
Well, the OP said "rapid decline". This is a gradual non-improvement, which is not the same thing.
Also, does going to school 7 days a week increase learning? I can sit in front of my computer and type stuff for 24 hours straight. Doesn't mean the result is any good.