“退学”常见的英文表达有 drop out of school 或 withdraw from school。
drop out of school： 侧重于表达主动放弃学业，不再继续在学校学习，是比较常用、口语化的表达。例如：He decided to drop out of school and start his own business.（他决定退学去创业。）
withdraw from school： “withdraw”有“撤回、退出”的意思，“withdraw from school”更正式一些，强调从学校这个机构中正式退出。例如：Due to health problems, she had to withdraw from school.（由于健康问题，她不得不退学。 ）