I disagree. I understand that American kids are behind when it comes to education but I dont think more time in school will fix that problem.
I think we should concentrate on using the time more efficiently as opposed to adding more time. If kids are going through a whole year learning nothing, adding 4 extra weeks won't help them.
But then how do address the fact that poor kids lose two months work of reading on average during the summer and kids of all income brackets lose math skills. I don't even see it as more school as opposed to reallocating how the hours are used. Use time more efficiently, keep them in class less because at a certain point people just zone out and don't give them 3 straight months of doing nothing. People are taking it the wrong way or not fully getting the alternatives. This would just be one part of a larger process. I'd link an article on Finland, but no one wants to read all that.