Push-ups are a great way to build upper body strength, but it's not fun to "drop and give 20." You can have students hold themselves up with both arms and take turns tapping one hand on the opposite shoulder while reciting the alphabet or alternating lifting hands and tapping a ball.
You can set up fitness stations around the gym. Some popular ones include jumping rope, jumping over small hurdles, front and back somersaults on a mat, a crunch station and a jumping jacks station. You can assign students to groups and have them rotate around the gym and play music while they're working out.
Groups like MarathonKids have curricula that teachers can use to get all of their students to run the distance of a marathon over six months. While this might be difficult for younger elementary students, fifth graders can easily cover the distance and can also appreciate the nutritional information that comes with the lessons offered by the groups. The Oklahoma City Marathon, held at the end of April each year, offers kids the chance to do their last 1.2 miles as part of the race festivities and earn a marathon finisher's medal.
As elementary school students prepare to participate in athletics and select sports, teaching warmup technique is crucial. There are many different dance routines you can lead students through that will warm up muscles in a dynamic way -- more effective and more fun than cold stretching. In addition to dance routines, you can prepare students for workouts by giving them a set of warmup drills to do at the beginning of each PE period and assigning different class members to be the warmup leader of the day. Age-appropriate drills include "high-knee" steps, lunges, "karaoke" (shuffling sideways, alternating hips out and back) and "butt kicks" (kicking oneself in the rear end at the end of each step, making each step very short).