Hanazakari no Kimitachi e

This hilarious comedy follows the chaos, troubles, and friendship at a boys' boarding school after a girl disguised as a boy joins. Ashiya Mizuki has just come back to Japan from California where she was raised. She fell in love with Sano Izumi, a hopeful high jump hero, who has quit after an accident. As she wants him to go back to the sport once again, she enters the same high school as a boy! With short hair, a flattened chest, and lowered voice, she starts sharing the same room with Sano.
(Source: DramaWiki)
~~ Adapted from the manga “Hanazakari no Kimitachi e” (花ざかりの君たちへ) by Nakajo Hisaya (中条比紗也).