Your kid's been hitting the books hard all week, but her latest spelling test is less than stellar. She's been studying, eating well and sleeping, so what could be the culprit?

If your little one is more likely to veg in front of a computer than run around during her breaks from schoolwork, her physical inactivity may be affecting more than her athletic prowess. A 2012 study conducted by the Picard Center for Child Development and Lifelong Learning at the University of Louisiana at Lafayette suggests that children with high levels of cardiovascular fitness scored up to 5 percent better on standardized tests than their less-fit counterparts.

If you're looking to schools to take action as well, you can think again. As recess time continues to dwindle and school lets out for summer, the burden shifts to parents to keep kids active. Classics like baseball, soccer, and football are great, but there's also a lot of less-popular activities to help children have fun and break a sweat. Take advantage of the summer heat and mix things up with these engaging cardio exercises for kids.

  • Swimming. Whether she's a Natalie Coughlin-wannabe or more of a cannon-ball extraordinaire, your kid will reap huge benefits from spending long hours in the water this summer. Use the upcoming Olympic games as a way to get your budding medalist fired up about being in the pool. Teaching different swimming strokes, diving and water games are great ways to use the swimming pool to get your kid's blood pumping.
  • Biking. Your neighborhood need not be a Tour de France course for you and your tiny cyclist to benefit from biking: a 125-pound adult burns an average of 450 calories an hour while pounding the pedals. To get the most bang for your bicycling buck, try swapping your car for your bike next time you need to take a family trip to somewhere nearby. Be sure always strap on a helmet, whether its a quick trip to the park or a lengthy ride. Look for models that are approved by the Consumer Product Safety Commission (CPSC) or Snell Foundation.
  • Rollerblading. Bring back this favorite eighties pastime when you hook your kid up with her very own set of skates. Mix things up by creating obstacle courses with traffic cones and chalk in your driveway, and encourage the little neighborhood group to come up with mazes to skate through. Whatever your plan, be sure your child's fully protected with helmets and body pads.
  • Jump Rope. It's time for double-dutch! Dust off that jump rope in the garage and teach your kid some of your favorite jump rope singalongs. Keep things hopping with fast-paced games like Snake, and encourage your child to come up with more rope-related fun with her friends.
  • Surfing. 'Tis the season for hanging ten! If you're anywhere near the beach and feel up to braving the waves, sign up for a parent-child surfing class. You and your kid will not only get tons of exercise, but learning to do something together will strengthen your bond and force you to lean on each other for support—both literally and figuratively!
  • Frisbee. Keep a Frisbee stashed in the back of your car so you'll always have a way to get some cardio in with your kids. When playing with the disc, keep in mind the most important rule: there are no rules! Encourage your little one to get silly with different throws, or help her set up different games with pals for friendly (and heart-healthy) competition.
  • Hiking. Whether you've got a couple hours or an entire day, hiking's a way to bond with your kid while snagging some serious exercise. If you're just starting out, search out short hikes and then work your way up to more serious climbs as you gain confidence. Amp up the education factor by researching and identifying plants as you go; before long, you'll be seasoned trailblazers with serious botany chops.
  • Dance. If your kid's summer schedule is looking soft in the physical activity department, sign your budding ballerina up for a dance class to get her in the groove. Dancing is not only a cardio workout, but also a fantastic chance to stretch muscles and release tension. If classic ballet isn't your thing, consider trying jazz, tap, ballroom dance, or even Zumba.
  • Volleyball. Bump, set, spike! Thanks to the upcoming Olympics, this popular beach sport is sure to appeal to any summer-loving kid. This sport requires quick thinking, fast footwork, and strong hand-eye coordination, making it an ideal way to strengthen both the mind and the body on a sunny beach day!
  • Yoga. Though you may not think it's a serious workout, an intense yoga class can torch a few hundred calories an hour while improving presence of mind, breathing, balance, and strength. For a beginning workout that won't overwhelm young ones, try Ananda or Hatha yoga. Once you become seasoned yogis, master more advanced moves with Bikram or Vinyasa classes.

Give yourself a pat on the back; between bouncing to music in dance or hiking serenely in nature, you're ready to tackle cardio exercises for kids this summer. Fostering a love of physical activity in your child will not only encourage her to get moving in the sun, but she'll also reap rewards when school starts back up in the fall. Win-win!