Will longer school year help or hurt US students?

Julie Carr Smyth:

Did your kids moan that winter break was way too short as you got them ready for the first day back in school? They might get their wish of more holiday time off under proposals catching on around the country to lengthen the school year.
But there’s a catch: a much shorter summer vacation.
Education Secretary Arne Duncan, a chief proponent of the longer school year, says American students have fallen behind the world academically.
“Whether educators have more time to enrich instruction or students have more time to learn how to play an instrument and write computer code, adding meaningful in-school hours is a critical investment that better prepares children to be successful in the 21st century,” he said in December when five states announced they would add at least 300 hours to the academic calendar in some schools beginning this year.