I generally prefer single-sex education, to be honest.
English school subject is one with many variations from one student to others: they may have many varied levels of English.
And my experience is that there are more girls that get better grades (or marks in UK) than boys.
Besides if we have only boys (for example), we avoid the problem of them trying to show off before girl classmates.
If we have only boys, we can focus on more restricted varieties of levels amongst them. It’s one more option, and now I remember an English teacher (he’s British and Spanish too I guess) that also told me he preferred single-sex education. He was a teacher we hired as a summer English camp, some years ago. / Photo from: women-hand-holding-umbrella-walking-in-the-winter-rain-on-a-street-in-Shanghai-city www magic4walls com. the picture is just an illustration