首先，以下是各學級的英文:
school = 泛指任何學校
primary school = elementary school = grade school = 小學
junior high school = middle school = 初中/國中
high school = 高中
college = university = 大學
再來，她是小我三屆的學妹，可以說:
She's three years my junior in (my) school. (my 可以更確認是同一個學校，但不用也行。)
也可以不提年份，直接說:
She's my junior in (my) school.
以下是另一種說法。我跟她在同一所大學，她是小我一屆的學妹:
She is one year behind me in college. (常用)
She is one year my junior in college. (常用)
以下有更多例句:
我的小我一年的國中學妹正在追我 = A girl who's one year my junior in middle school is pursuing me. = A girl who's one year behind me in middle school is pursuing me.
我的大學學妹正在追我 = My junior in college is pursuing me.
She is two years behind me in school = 她是我學妹，小我兩年
另外，We went to the same college. She was a senior. I was a freshman. 就表示她是12年級，我是9九年級。
以下說法表示我們去同一個學校求學過:
We went to the same school.
We were in school together.
順道一提，alumni 是指校友，但你不能說 She's my alumni. 可以說 She's a fellow alumni. 或 She's a fellow alumnus. 詳情請猜考
「校友」的英文怎麼說。
注意，upperclassmen 不指學長或學姊；underclassmen 也不指學弟或學妹。
