drop out

to not do something that you were going to do, or to stop doing something before you have completely finished:
He dropped out of the race after two laps.

If a student drops out, they stop going to classes before they have finished their course.

アメリカ英語辞典
to stop going to school before finishing the course of instruction:
He dropped out of school when he was 16.

(Cambridge Academic Content Dictionary からの drop out の定義 © Cambridge University Press)

ビジネス英語
to not do something you were planning to do, or to stop doing something before you have finished:
Some bidders are rumoured to have dropped out because of the cost of putting the company back on its feet.
drop out of sth He dropped out of school a month before graduation .
(Cambridge ビジネス英語辞典 からの drop out の定義 © Cambridge University Press)

- Cambridge Dictionary