drop in :顺便拜访一下.
drop out :to withdraw from 退出.
如:He has decided to drop out of politics.
他已经决定退出政坛.
Seven students dropped out of university last year.
去年有七个学生被退了学.
找到的句子:
Last chance high :how girls and boys drop in and out of alternative schools
要放在句子里才翻译得通,没有背景,只能在上面找找了