The purpose of this study was to clarify changes in high jump (scissors jump) performance in physical education classes for junior high school students in order to suggest training optimization according to grade. High jump lessons were conducted 8 times, and the scissors jump motions of the subjects were captured by 2 cameras (60 fps), both fixed and panned, in the first (pretest) and last (posttest) classes. The motions of the subjects were analyzed in 3 dimensions using the panning DLT method. The subjects were 22 students who were divided into 2 groups: 1st and 2nd grade students who learned the high jump as a compulsory subject, and 3rd grade students who did so as an optional subject. The main results were as follows: (1) In both groups, whereas the mean approach run speed was significantly decreased, the best records were significantly improved. (2) In 1st and 2nd grade students, the change in the ankle joint angle of the take-off leg during the take-off phase was smaller in the posttest than in the pretest. In addition, the knee joints of both legs during the jumping phase were more extended in the posttest than in the pretest. (3) In 3rd grade students, the take-off angle was significantly increased, and moreover the rate of conversion of the horizontal velocity of the center of body mass (COM) at the start of the take-off phase into the COM vertical velocity at take-off was significantly increased. This increase in the conversion rate was related to a significant increase in the knee extension velocity of the take-off leg during the take-off movement. In 3rd grade students, a more pronounced rhythm was observed in the last 2 steps of the approach run during the posttest. From these results, we suggest that for 1st and 2nd grade students, emphasis should be placed on the technique for obtaining rhythm in the approach run, whereas for 3rd grade students, there should be a focus on the take-off movement, making good use of the approach run speed.