I don't think this is the worst idea out there, but I don't see how it helps that much either. Imagine, instead of extending the day or the school year, we added a 13th grade to the end of high school. I'd think that the kids who already benefit from their educations would learn a little more, but the ones who we've failed to make literate or numerate or rational or intellectually curious in their first 13 years wouldn't suddenly be pushed over the hump with another year of the same thing that hasn't worked for them already.
Are there that many people at the margin that would benefit from X extra hours of the same instruction, whether you add it a little each day, a little each year or all in one extra year? Maybe there are. It's a semi-empirical question. (Walker points to some data that says the results are decidedly mixed.) I don't know that much about pedagogy, but I think it would make sense to look into some changes besides "more of the same."
I'd also say there's a ton of waste in the calendar as is. After you subtract time for testing and exams, holidays, lost time at the shoulders of holidays, assemblies, field trips, half days where nothing gets done because classes are too short and attention is elsewhere, etc. you get maybe 120 days of instruction out of a 180 day school calendar. You could add another month to the calendar at no cost by being rigorous and cutting that non-instructional time in school in half. (I had one math teacher who gave us a test every week. I think it was Wednesdays. He burnt through 20% of the school year just giving us tests. And he wasn't even the most wasteful teacher I had. I can not discuss in polite company the absurdity of Mrs Baez's Spanish classes.) Of course that puts the burden on teachers and administrators to be very disciplined. Who's going to step up to the plate and say "no, my students will not be missing class to go listen to an assembly about traditional Peruvian drumming*" or "no, you can not put Spartacus on for the entire week before Christmas break and call it 'teaching Latin.'" I'm not sure where the incentive to do that is going to come from in a public school.
* We actually had one of those in high school. Hour and a half long. I'm not making this up.
Walker also asks at the end of his post:
Cliché query: Does anyone actually find it compelling to hear the phrase "21st century" appended to any word the speaker wants to stress, as though there were some sort of sea change on December 31, 2000?Absolutely not. I'm curious to see how long into the century politicians and commentators will be able use that crutch.