「私の行った学校は制服がありませんでした」を英語でいうときには、「① The school I went to didn't have uniforms.」と言います。
制服はもちろん、Uniformと言います。語源として、Uni = 均一、Form=形。
Unisexも同じ風に考えればわかりやすいと思います。
ジュリアン
>We wear casual clothes to school.
*casual clothes=without formality of style or manner, in particular (of clothing) suitable for everyday wear rather than formal occasions.
>We do not have a set uniform at our school.
*set= establish as (an example) for others to follow
*uniform= the distinctive clothing
We wear casual clothes to school.
「casual clothes」とは、フォーマルではなく、普段着ているような服装のことです。
We do not have a set uniform at our school.
「set」とは、 規則や決められたという意味です。
「uniform」とは、決められた服装を意味します。
My school didn't require its students to wear uniforms.
"I wasn't required to wear a uniform at my school."
"require to" is used to show obligation, where there is not a choice given to do something. It must be done.
"I wasn't required to wear a uniform at my school."
〔訳〕私の学校では制服を着なくてよかった
「require to」は義務を表します。選択肢がない、それをしなければならない、ということです。
Mufti day = A mufti day (also known as casual clothes day, casual Friday, colour day, own clothes day, home clothes day, plain clothes day, non-uniform day, mufting day, free dress day, civvies day, dress down day, uniform-free day) is a day where students and staff go to school in casual clothing instead of school uniform.
Casual clothes are clothes which you are comfortable in.
Most schools require their students to wear uniforms, require meaning in this context that it is obligatory, which means there is no choice about it. So to say that your school 'did not' require you to wear uniforms, explains that you were not obliged to wear them.
大半の学校では、制服の着用が義務づけ（require）られています。「require」はここでは「obligatory（選択肢がない）」という意味です。
ですから：
My high school didn't require us to wear uniforms
↑制服を着る義務がなかった、という意味になります。
I didn't have to wear school uniforms in my high school days.
Our high school had no school uniforms.
私たちの高校には制服はありませんでした。
このように表現するのが最もシンプルで自然かと思いますよ！
I didn't have to wear school uniforms in my high school days.
私は高校時代は制服を着る必要はありませんでした。
制服を進んで着るというよりは、着なければいけないものという
話し手のニュアンスが入る表現です。
We can talk about this either using the verb, "to have," or, "to require," to show that it's something our school had or didn't have. We can also use the phrase, "had no school uniform," to come out with the same meaning.
日本 
イギリス 
南アフリカ 
アメリカ合衆国 
