The Romantic President

The Romantic President Hangul , lit. The President who Plays the Piano is a 2002 South Korean film. It stars Ahn Sungki, Choi Jiwoo, Im Soojung and was directed by Jeon Manbae.

A scene showed Choi entering the class, disguised as a new student. Choi sat beside a girl as she acted blatantly and introduced herself as a transfer student. With the girls help, Choi identified the exceptional students, from the rebel to the most studious student and so on. Choi left the classroom shortly before the class started.The students ran back to their seats as the principal introduced their new teacher. They were shocked when Choi, who had disguised herself as a transfer student earlier on, was their new teacher. ........

Source: Wikipedia