「教え子」はシンプルに my student や a student of mine が自然な表現です。
日本語では、過去に教えたことがある人物に関しても「教え子」と言いますが、英語だとちょっと違います。「元生徒」という意味で、a former student や a former student of mine、他には「教えていた子（のひとり）」で、one of the kids I taught や one of the kids I used to teach もOKです。
こんにちは！
「教え子」は student や pupil ということができます。
student も pupil もどちらも「学生」「生徒」という意味です。
どちらかといえば student の方がよく聞くかと思います。
例：
He is one of my former students.
彼は私の元教え子なの。
These are my students!
この子達が私の教え子たち！
ぜひ参考にしてください。
まず「教え子」という名詞の表現ですが、
the people I taught in school
でいかがでしょうか。
また、もし別に名詞で「教え子」という言い方を
しなくてもＯＫな場合であれば、例えば以下のように
言うのもいいかなと思います。
I used to teach them.
彼らは教え子なんです。
Student
A person who is studying at a university or another institution of higher education.
example - The student studies at a law school.
Learner
A person who is learning a subject or a skill
example - the learner is being taught trigonometry.
Pupil
A person who is taught by another, especially a schoolchild or student in relation to a teacher.
Student
大学やその他の高等教育機関で勉強している人。
例 - The student studies at a law school.（その学生はロースクールで勉強しています）
Learner
科目やスキルを習得している人
例 - the learner is being taught trigonometry. （学習者は三角法を教えられている）
Pupil
誰かに教わる人、特に教師に対する小学生や生徒
Even when you are a grown-up/adult, your school teacher will always call you a student/learner or pupil.
"Many years ago, he was a learner of mine."
"He was my favorite pupil."
"This was my best English student."
大人だとしても、学校の先生はstudent/learnerまたはpupilと呼びます。
"Many years ago, he was a learner of mine."（何年も前、彼は私の教え子でした）
"He was my favorite pupil."（彼は私のお気に入りの生徒でした）
"This was my best English student."（私の一番の英語の教え子です）
All of these words describe children/teenagers/young adults that are taught by teachers.
By adding the word "past" eg "past pupil" this explains that the teacher taught them before but is not currently teaching them.
In England they are called students or pupils in schools.
Adults (18+) are usually referred to as learners.
I had a lot of students in my class today at school.
Many of my pupils were late for school.
My learners at the university are very inquisitive.
Hope this helps
Jane:)
イングランドの学校では students や pupils と呼びます。大人（18歳以上）の場合は learners と呼ばれます。
例
I had a lot of students in my class today at school.
（今日は学校で私のクラスにたくさんの生徒がいた。）
Many of my pupils were late for school.
（私の生徒はたくさん学校に遅刻した。）
My learners at the university are very inquisitive.
（大学の私の教え子たちは、とても探究心がある。）
参考になれば幸いです。
Pupil = a student who is taught by a teacher, especially a young student
Student = a person following a course of study, as in a school, college, university
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Examples :
He usually walked home with a girl pupil.
Two pupils and a teacher were injured.
Parents might wish to buy a home for student children away at university.
My daughter is a good student who enjoys school.
Pupil = 生徒、特に若い生徒。
Student =学校、短大、大学、カレッジで学ぶ生徒
------------------------------------------------------
例:
He usually walked home with a girl pupil.
彼は通常、女生徒を歩いて自宅まで送っている
Two pupils and a teacher were injured.
２人の生徒と１人の教師が負傷した
Parents might wish to buy a home for student children away at university.
大学から遠くにいる学生の子供のために家を買いたいと親は思うかもしれない。
My daughter is a good student who enjoys school.
私の娘は学校を楽しむよい生徒です。
アメリカ合衆国 
日本 
南アフリカ 
イギリス 
