When you send your kid to dance class, it’s reasonable to think that not only are they learning how to dance, but that they are getting exercise. Most parents think that way; dance class certainly gets mentioned when I ask parents in my practice what their children do for exercise.

Not so much, says a study just published in the journal Pediatrics.

Researchers studied 264 girls — 154 children and 110 adolescents — taking dance class in 17 private studios and four community centers in the San Diego area. They found that the girls averaged only 17 minutes of moderate-to-vigorous physical activity each class.

In retrospect, I do remember that when I used to pick my daughter up from dance class she was rarely, if ever, sweaty. Guess that should have been a red flag.

Younger girls were more active than adolescents, which I found interesting — I think of adolescents as being more intense about dance class. They also found that of the different kinds of dance classes they studied (ballet, tap, jazz, partnered dance, hip-hop, Latin flamenco and Latin salsa and ballet folklorico), kids at the hip-hop ones were most active.

This isn’t necessarily a big deal if the point of the dance class really is just to learn the dance and if your kids are active in other ways. But if it’s all your kid does for exercise outside of school, well, it is kind of a big deal. Seventeen minutes isn’t going to cut it for cardiovascular health and staying at a healthy weight.

Oh, and that exercise at school thing? For most schools, that’s a “not so much” thing too. In fact, another study in the same journal found that preschoolers at 10 childcare centers in Seattle spent less than a half hour a day being moderately-to-vigorously active. This is preschool, which we think of as mostly playtime.

For me as a pediatrician, the take-home is that parents need to a) choose activities and programs carefully, and b) not take it for granted that their kids are active where and when they would expect them to be, and c) need to be really proactive about getting their kids active.

Shut off the TV, send them outside to play if you’ve got a yard, bring them to the park, sign them up for sports, go for family walks and bike rides. Honestly, exercise is what makes all the difference when it comes to health now and in the future — and the habits we learn in childhood tend to stick with us.

Don’t leave it up to dance class — or gym class. It’s up to you.

Claire McCarthy is a pediatrician at Boston Children’s Hospital. She blogs at the Huffington Post, where this article originally appeared, and at Boston.com as MD Mama.

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