This graphic is a little puzzling. It looks like South Korea spends half the instructional hours on math that we do for a significant increase in math scores at age 15. Doesn't that suggest that maybe we should spend less time than we do. What are we doing with all that time on math? Are we harming some students? It looks like there is a fairly decent correlation of age 15 scores with total school days, except for Brazil. And look at Mexico, they spend more time and score lower than we do.
The article points out various strategies and tactics for avoiding this 'summer slide,' many of which look promising. What took them so long? Maybe we should post the math skills that need to be understood and when they have been demonstrated then the student gets to do something else. Some might finish by age 14, while others might take a few more years. Maybe the end point should be when the student is capable of showing that his parents understand the concepts.
I remember Time Magazine as a sort of middle of the road weekly news magazine for average working stiffs who didn't have time to listen to NPR. I'm not sure what audience it is aiming at these days.