A school where both boys and girls study is called co-ed (co-education) What is the name for the school where only males study? (Calling it a male school seems a bit awkward)
In the UK, such schools are called boys' schools.
St James Senior Boys’ School in Ashford, TW15, offers a distinctive philosophical education ...
It's also possible to describe such as a school as an all-boys school, but Brits are just as likely to say "boys' school":
Rupert's at an all-boys school — St James Boys' School in Ashford.
Horatio is at a certain boys' school in Harrow.
Using all-boys emphasises the nature of the school as a single-sex school over the simple adjective boys'.
A school for boys is a boys' school and one for girls is a girls' school, although the trend in the language, as noted in the answers to “Boys bicycle” vs. “boy's bicycle” and User’s/Users’/Users Group and others, is to drop the apostrophe; thus boys school and girls school are increasingly common.
As coeducation is the norm for most people in most English-speaking countries, the meaning of school for boys or school for girls is also clear, though at least in North America, it would be more common to describe such an institution as an all-boys school (or all-girls school).
The term for the practice of teaching the two genders separetly, regardless of the gender we might be talking about is:
Single-Sex Education or Single-Gender Education or Single-Sec Schooling. Source: wiki
For specific institution catering to one specific gender-
The Boarding School Review uses the terms All-Boys and All-Girls to refer to as the Student Body type for single-sex institutions, here.
Using the search function above, the websites of single-sex institutions shows that the websites themselves rarely use a term for that aspect of their student body - either there's no explicit mention of the school being all-boys outside of admission qualifications, or terms like "Educating Young Men since..." etc are used.
The wikipedia category for these schools in the US is simply "Boys' Schools" (the all does seem a bit redundant), and the articles themselves use a mix of All-Boys or Boys' Schools as terminology.
- Archbishop Riordan High School is an ... all-boys Catholic high school.. in San Francisco.
- Newington College is a ... day and boarding school for boys... in Australia
- Ardscoil Rís is a boys' secondary school in ... Dublin, Ireland
- Catholic High School (traditional Chinese: 公敎中學) ... is an all-boys Catholic school in Singapore.
- Nyeri High School', also known as Nyeri High, is a boys' boarding school ... in Nyeri, Kenya.
First, note that single-sex schools are waning in the UK. In 1966, there were 2,500; in 2006, there were just 400. There's public debate at the moment because some (mainly immigrant) minority communities approve of segregation, but mainstream society and the legislature are pushing hard "to open" established single-sex schools and up prevent new ones being set up.
So in most contexts in the UK today, any reference to a segregated school (by sex, religion, race) is likely to be somewhat pejorative/disparaging. But 50 years ago when I went to the local State-run boys' school (which was just down the road from the affiliated girls' school), those were perfectly normal ways to refer to what were at the time perfectly normal schools. Today it simply wouldn't be possible to use either term without risking unwanted connotations being perceived.