ATLANTA, Georgia (CNN) -- You would expect to find pre-algebra, American history and grammar in a middle-school curriculum, but what about a lifetime lesson in fitness?
It's important that adolescents and younger kids use low amounts of weight and proper form in strength training.
At a time when childhood obesity is reaching epidemic proportions, an increasing number of schools are paying closer attention to what's being taught during physical education.
Pace Academy in Atlanta, Georgia, is one such school. On any weekday morning, the school's weight room is humming. The private school facility looks like a regular gym for adults, but on this day a dozen or so 11- and 12-year-old boys are working the leg press and bicep machines like pros.
Teacher and coach Kris Palmerton, who also serves as the school's athletic director, works the room, adjusting equipment and correcting the students' technique. "This is the time to introduce them to strength training, the importance of fitness for a lifetime," he says.
While these preteens may not worry about it now, the exercises can lead to better heart and lung function, lower cholesterol, stronger bones and a fitness habit that could last well beyond the seventh grade.
Palmerton reassures students and their parents that the introduction to strength training program is not to be confused with weightlifting or bodybuilding.
"We want to increase their flexibility, which is extremely important in their growth and development," Palmerton says. "Everything we do is high repetitions and very low weight. We're certainly not trying to increase muscle mass at this age," which he says would put inappropriate pressure on the growth plates.
Growth plates are areas of cartilage that have not yet turned to bone. Some doctors worry that they can be strained during heavy lifting. Young muscles and tendons are also susceptible to injury. Watch more on strength training for middle-schoolers. »
The American Academy of Pediatrics supports strength training so long as proper techniques and safety precautions are followed. The group warns pre-adolescents and adolescents to:
1) Get a complete checkup by a pediatrician before starting a formal strength training program.
2) Include time for warming up and cooling down.
3) Any injury or illness should be evaluated before continuing with the program.
The National Strength and Conditioning Association issued similar recommendations and recommends students be closely supervised.
Palmerton keeps a close eye on his class, watching for mistakes or clumsy moves. He finds the biggest problem is reminding the kids to adjust the equipment to their body weight and size.
"The key is learning how to use the machines properly," he says, "as well as proper extension and contraction of movements, so they're training the muscle right and getting it all done with a very light weight."
Not all schools can afford fancy workout equipment. Palmerton says similar strength training results can be achieved through students using their own body weight and doing old-fashioned calisthenics. Sit-ups, push-ups and plyometric drills -- exercises that involve repeated rapid stretching and contracting of muscles to increase muscle power, such as squats and jumping -- can promote strength, flexibility and speed.
Palmerton tells students the exercises will help their performance in other sports. He also reminds them that good strength-training skills can be useful in adulthood, long after they've finished competing on a soccer field or running track.
"It's a foot in the door," concludes Palmerton. "It's a learning experience that they can definitely carry with them." E-mail to a friend
Judy Fortin is a correspondent with CNN Medical News.