The average height of male students in 2017
Elementary school 6th graders: South Korean is 151.9 cm, Japanese is 145.0 cm
Junior high school third grader: Korean is 170.1 cm, Japanese is 165.3 cm
High school third grader: Korean is 173.5 cm, Japanese is 170.6 cm

Average height of female students in 2017
Elementary school sixth grade: Korean is 152.3 cm, Japanese is 146.7 cm
Junior high school third grader: Korean is 159.9 cm, Japanese is 156.5 cm
High school third grader: Korean is 160.8 cm, Japanese is 157.8 cm

Male student average weight in 2017
Elementary school 6th graders: Korean is 48.1 kg, Japanese is 38.2 kg
Junior high school third grader: Korean is 63.6 kg, Japanese is 53.9 kg
High school third grade: Korean is 71.0 kg, Japanese is 62.6 kg

Average weight of female students in 2017
Elementary school 6th graders: Korean is 45.8 kg, Japanese is 39.0 kg
Junior high school third grader: Korean is 54.5 kg, Japanese is 50.0 kg
High school third grader: Korean is 57.8 kg, Japanese is 53.0 kg

Source
https://m.post.naver.com/viewer/postView.nhn?volumeNo=14113419&memberNo=34856962
http://www.mext.go.jp/component/b_menu/other/__icsFiles/afieldfile/2018/03/26/1399281_03_1.pdf