On a morning in late September, the headteacher of Ysgol Bro Hyddgen, Gareth Llwyd, stood in the school's lower yard in Machynlleth, Powys, and greeted 412 pupils, every one of them, in Welsh.

He has done this every morning he has been at the school, which is sixteen years. He says it is the easiest part of his day.

Ysgol Bro Hyddgen is what is known in Wales as a cyfrwng Cymraeg school: every subject, from mathematics to physical education to ICT, is taught through the medium of Welsh.

Most of the children at the school did not speak Welsh at home as their first language. About forty percent did. The rest acquired it at school.

By the end of Year 2, around age seven, the school's internal assessments find that nearly all of them are functionally bilingual.

By the end of Year 6, around age eleven, the difference between the home-Welsh and the school-Welsh children, on most measures, is no longer statistically detectable.

What happens to those children after they leave, however, has been less clear, until recently.

Since 2008, a research team based at Bangor University, led by the linguist Dr. Rhiannon Ellis-Powell, has tracked a cohort of 287 graduates of Ysgol Bro Hyddgen and three similar schools.

The cohort entered Year 7 in 2008. The youngest are now thirty. The team has interviewed each of them, on average, every three years.

“The team has interviewed each of them, on average, every three years.”

The most recent report, published in February, traced what had become of their Welsh.

Of the 287 graduates, 274 were still living. Of those, 261 reported using Welsh at least weekly. 198 reported using it daily. 112 had children, and of those, 89 were raising their children in Welsh.

The graduates were not concentrated in Wales. Forty-one were living in England, eleven in Ireland, six in other parts of the world. Most of those still found someone to speak Welsh with, by phone or online, at least once a week.

Dr. Ellis-Powell's report is careful. It does not claim that the school produced the language use. The graduates came from communities where Welsh was already valued.

But the report does observe that the school appears to have given them, in her phrase, a working tongue rather than a heritage tongue.

One of the graduates is a woman named Lowri Pritchard, now thirty, a midwife at Bronglais Hospital in Aberystwyth. She entered Year 7 at Bro Hyddgen in 2008.

She did not grow up speaking Welsh. Her mother was from Birmingham; her father, from Llanidloes, had grown up English-speaking despite his own Welsh-speaking grandparents.

She delivers babies now in Welsh and in English, switching between them depending on the mother. She says she sometimes does not notice which she is speaking.

Another graduate, a software engineer named Iestyn Morris, lives in Lisbon. He works for a Portuguese fintech in English. He speaks Welsh on Wednesdays, by video call, with three friends from his Year 11 class.

He has done this since 2017. The call lasts about an hour. They talk about their week. Sometimes they talk about nothing in particular.

He told the Bangor researchers that he could not say whether the call mattered to him in any large way. He said only that he would not stop it.

The school itself, meanwhile, has its difficulties. Enrollment dipped during the pandemic and has only partially recovered. The building, parts of which date to 1894, needs a new roof.

Llwyd, the headteacher, is sanguine. He says schools have always needed roofs. He says the language is older than the roof and will outlast it.

He locks the gate at half past four each afternoon, walks through Machynlleth to the bridge over the Dyfi, and goes home.

On the walk, he sometimes meets parents of pupils, and they speak, almost always, in Welsh. He says this is not remarkable. He says it is simply Tuesday.