Adopting mixed-sex education

Under the rule of occupation by the Supreme Commander for the Allied Powers after World War II and the reformed School Education Act of Japan, former secondary schools were converted into Upper secondary schools [jp], established as part of the democratization policy. At that time many public schools with single-sex education were made into mixed-sex education with exception of some local public entity|local government including Miyagi prefecture, Fukushima prefecture, Gumma prefecture, and Saitama prefecture.^[8] Most private schools applying single-sex education reserved students' specification nationwide while they accepted conversion to upper secondary school, with cases of continued education through middle school and upper secondary school as a single system.

Rare cases were seen with those administrations of Yamaguchi Prefecture, where former high schools were integrated with nearby former secondary schools and transformed into upper secondary schools under a new school system. A typical case of Osaka Prefecture converted those upper secondary schools under its administration into the new system; however, instead of integrating with neighboring junior/upper secondary schools, they replaced the whole population of students and teachers in school A with those who had belonged to school B.

Amami Islands

Amami Islands left Japanese administrative power in 1946 (Showa 21), and the Provisional Government of Northern Ryukyu Islands (ja) introduced their new school system in 1949, delayed by one year.^[9]

Transition measures for the former primary and secondary education (1946–1950)

Public schools

Up to March 1946, compulsory education in the secondary level was offered up to the senior level at public National schools in Japan [ja] kokumin gakko kotoka (国民学校高等科), a level providing lower secondary education equivalent to Senior elementary school called Kōtō-shōgakkō (高等小学校). Graduates were admitted to those surviving Middle schools (ja) or chuto gakko (中等学校) under former system. All those who graduated from elementary schools after March 1947 (Showa 22) were admitted to the current Junior high schools in Japan [ja], or chugakko (中学校) for their lower secondary education. Starting in 1935, in some public primary schools, continued education for working youth was offered along with military drills at Youth Schools (in Japanese) or Seinen gakko (青年学校)(ja).

In August 1945, there were three sub-systems to middle schools; for boys kyusei chugakko (旧制中学校), for girls koto jogakko (高等女学校), and for both sexes vocational school jitsugyo gakko (実業学校). It was in April 1947 (Showa 22) a measure was taken to provide interim attached middle school (併設中学校, heisetsu chugakko) to each faculty of public middle school: although new students admitted in April 1947 were admitted to the current junior high schools at once, those entered middle school level in 1945 and 1946 (sophomore and senior students) were advanced to the attached middle schools as a transition phase to secondary higher education.

Private schools

The private middle schools were given choice of whether they will change to new school system at once, or to apply transitional system. There were cases that private schools decided to continue the attached middle school after 1950, and they offered continued six-year period of secondary education.

University of Tokyo Junior High School

During WWII, they suspended recruiting students for the former high school regular course (旧制高校尋常科), and in 1946 (Showa 21) very few public secondary schools admitted students as Tokyo koto gakko (東京高等学校) (ja) did, but none in 1947. The freshmen of 1946 became isolated as no new students followed them under former school regulation, and in their senior year in 1948 (Showa 23), the school was reformed into the University of Tokyo Junior High School, recruited new freshmen and sophomores to fill the classrooms. It is reformed later to become the current Secondary School of the Faculty of Education, the University of Tokyo [ja] affiliated to the University of Tokyo.

• 1946 (Showa 21)

• A 6th grader in shotoka, kokumin gakko (in Japanese) would enter a reformed junior high in 1947, then graduate and would enter an upper secondary in 1950;
• A 1st grader in Kotoka, kokumin gakko (in Japanese) would transfer to a 2nd grade in a reformed junior high in 1947, then graduate and would enter an upper secondary in 1949;
• A 1st grader at Youth school: in Futsuka (in Japanese) Regular course would transfer to a 2nd grade in a reformed junior high in 1947, then graduate and would enter an upper secondary in 1949;

Higher education : 1948–1950, converting to modern universities

Under the system former to reformation, the last students were admitted in spring of 1948; Kyusei kotogakko was introduced in 1894 and expired in 1950 after the reformation in 1918, Kyusei semmongakko (旧制専門学校) in 1903 as a single major normal school specializing in elementary school education was called Shihangakko (師範学校) with Koto shihangakko (高等師範学校) for training educators for high schools and college level.

Daigaku yoka (大学予科) along with Kyusei kotogakko had been established as the primary higher education for those who would continue to universities. For Kyusei kotogakko, the senior year graduates, or the 3rd graders who commenced from kotogakko in 1947 were the last generation finishing the full three years' term of high school education. Those freshmen entered in 1948 completed their first year under the former system, and as it expired at the end of the academic year 1948 or March 1949, they did not qualify to transfer for their choice of colleges under a new system, or shinsei daigaku (新制大学). They applied for admission examination and entered colleges and universities in the spring of 1949.

The idea of 1949 educational system reform was to reform so-called high schools under the old system as colleges and universities. As shinsei daigaku or universities under a new system, those high schools under the old system including single major semmon gakko and shihangakko for future educators were renamed.

For students, those who had studied for the full four years' term and qualify as kyusei chugakko (旧制中学校) graduates in 1947 were offered two options. They either could enter kyuseikoko and transfer, or enter shinsei koko, the present day high school and continue to prepare for college/ university. As for special transition measure, those 3rd graders in old high schools were also given those two options. Like on the Komaba campus of University of Tokyo, there were rivalry seen among those high school students of Daiichi Kotogakko against the university students. While the last kyusei daigaku, or old system universities admitted students till 1950, there were considerable number of graduates of old system high schools who either failed at the admission examinations or postponed their applications. Universities established administered by the new system held special examinations for those graduates of past academic years as transfer students.