Many were never expected to survive into adulthood. But at the reunion of Birmingham’s open-air schools this week, nearly 200 former pupils swapped stories about rest periods on stretchers in the snow, doses of cod-liver oil and classrooms so cold the ink froze in inkwells. And they insisted their school days really had been the happiest of their lives.

The guest of honour at Uffculme School in leafy Moseley, three miles from Birmingham city centre, was 90-year-old Ada Newsome, a pupil from 1915-1918.

“I used to go on the tram from Balsall Heath, we had tokens for the fare. We’d have breakfast of bread and milk or porridge. After morning lessons, we went to the resting shed, it was open all round, but there were boxes with blankets and pillows. We had to lie on the camp beds, they were canvas, and rest - you couldn’t read or anything. Then after an hour we had our lunch.

“In winter they issued us all with navy blue jumpers, mittens and clogs. We loved walking in the snow, we thought that was marvellous.”

Birmingham’s first open-air school, Uffculme, opened in 1911 to educate the city’s “delicate” children whose schooling had suffered due to malnutrition, asthma, bronchitis and other respiratory diseases. Many came from back-to-back houses in the slums. In the absence of effective drugs, the regime of nourishing diet, regular exercise and, above all, constant exposure to fresh air, was their only hope.

The classrooms were built with sliding screens, so three sides were open to the elements. Former teacher Moira Armson said that that proved problematic: “There was only one side that was solid and a third of that was blackboard with a little space for a book corner and just a tiny space for work. I suppose it let the teachers out of a lot of display work.

“I’d gone to see the school in the summer and thought it was great, but in winter I found the cold very hard. The children could run up and down to keep warm, but I got chilblains,” she said.

Pauline Saul attended Uffculme between 1951 and 1956. “I started there in January and my enduring memory is of the bitter cold. My hands and feet used to swell and when I came home at night my mother could hardly take my shoes off. But after a few months I gradually got used to it and I enjoyed the open air, even when it was cold.”

The memories prompted Pauline and her Uffculme contemporary Frances Wilmot to write a history of Birmingham’s six open-air schools. A Breath of Fresh Air draws on log books and photographs as well as the memories of pupils and staff to provide a comprehensive account of a movement largely ignored by historians.

A log book entry from 1924 for Cropwood, a residential school in the Lickey Hills outside Birmingham, describes the pupils: “For the most part they are of a very low standard of physique and are dull and lethargic. The weather is very severe with hard frost and snow. Frequent physical exercises are being given at regular intervals during lessons.”

Diet and the children’s weight were a worry. Uffculme’s log book in November 1911 records: “Since the cold weather set in children have not shown a good increase in weight. We have therefore changed the menu giving them suet boiled in milk at breakfast and suet pudding three times a week at dinner. Also treacle in place of sugar in the porridge and an apple with bread and milk. The results have been most satisfactory.”

Indeed, despite the hardships, the fresh air cure appeared to benefit most of the pupils - during the First World War, Uffculme was the only school in Birmingham to stay open when an influenza epidemic hit the city.

Five further open-air schools, four of them residential, were founded in the countryside around Birmingham.

James Robertson was transplanted from an inner-city, back-to-back house to Hunter’s Hill residential school in 1950. “I remember the camaraderie and all the sport. They encouraged us to play football, cricket and go for endless walks. The whole school would go blackberry picking and fill about 10 huge silver canteens with fruit and then we’d have blackberry pie for the next month.”

The prominence of the chocolate drink in building up the children is not surprising given the influence of the Cadbury family on the city’s open-air schools.

Uffculme was built with land and money offered to the city by Geraldine and Barrow Cadbury, whose son Paul had suffered from suspected tuberculosis. He recovered after the whole family moved to their holiday home, Cropwood, which was adapted to create open-air bedrooms. Cropwood became Birmingham’s first residential open-air school in 1922.

Jenny Cangy became a pupil at Cropwood in 1958. “When you arrived you were bathed, they checked your hair for nits, and then they kitted you out with clothes. Your clothes were identified by number and I was number 74. I had that on my knickers, my socks, my nailbrush, my toothbrush, my face flannel, but it wasn’t a case of come in number 74, we were all known as individuals and the big girls looked after the little girls.”

By the 1960s, drug treatments were being developed for many of the conditions the open-air schools had been established to tackle and “delicate” children were being admitted to mainstream schools. Though most former pupils doubted that today’s centrally-heated children would tolerate the conditions, Gillian Royle, the last headteacher of Haseley Hall, spoke for many at the reunion in mourning the loss of the open-air system.

“I suppose they were spartan in some ways but the children were well-clad and cared for. I think it’s a tragedy they’ve disappeared.”

Kate Harrison is the education correspondent for BBC West Midlands. A Breath of Fresh Air by Frances Wilmot amp; Pauline Saul, is published by Phillimore and Co at pound;30.