The low level of fitness in junior-high school students is an area of great concern. An important, but misunderstood, part of the physical education curriculum is the development of aerobic fitness. What is the best way to go about developing aerobic fitness? Four groups of primarily Caucasian (79.9%) Grade 8 and 9 students (n = 144), attending a large Grade 8-12 school in a suburban west coast Canadian city were tested using a pre- and posttest comparison of one of four instructional formats to determine which produced the greatest increase in aerobic fitness as measured by two timed 2400 meter (1.49 miles) running tests 10 weeks apart. A secondary goal was to see if there existed any difference between boys and girls in fitness attainment. The results indicated that the group receiving the instructional format with the varied activities showed a significantly greater improvement (p less than 0.05) in aerobic fitness than the other three groups. This would support the idea that providing varied activities that are fun and engaging is beneficial in increasing aerobic fitness in junior high school students. The results also showed that there were no significant differences between boys and girls as to treatment method. (Contains 2 tables and 3 figures.)