It’s an increasingly common mantra: longer school days and years are needed if students are to compete in a global, competitive world. In fact, five states just announced they’ll be adding 300 more hours to schools calendars: Colorado, Connecticut, Massachusetts, New York and Tennessee

As with so many things, this idea sounds good, but before parents sign on, they should ask a few questions.

First, how much time is already lost by design because of school district calendars? Think of all the teacher in-service days, where students are released early for example.

Then when they are actually in school, how many pizza parties, holiday parties, field trips, in-school productions are there? Everyone likes a bit of fun, but it’s worth asking how much actual learning time is compromised.

Next, how good is your child’s teacher? That’s the number one in-school factor contributing to student learning.

As schools near you likely scramble to add extra hours to the school day and year, consider: American schools already clock in more instructional hours than any other industrial country: close to 1,100 a year.

Contrast that with other countries that routinely outperform American students: Germany and the Netherlands, around 773 hours; Finland, 600; Korea, 575. Japan, 500 teaching hours per school year.

As with most things, quality trumps quantity.