"It didn't mean anything to us," he says, recalling his upbringing at 262 Scotland Street, a tenement that was across the road from the school but was torn down long ago.
Gus Macdonald, the former broadcaster and government minister who took the title Lord Macdonald of Tradeston from the area where he grew up, became a pupil at the school a decade later, in 1945.
"I was aware that the school was different," he says. "We knew there was something strange but nobody had heard of Mackintosh then. It was only much later when a friend of mine, Murray Grigor, made one of the first programmes about Mackintosh that I became aware of who had designed the school."
That programme helped to thrust Mackintosh into the Scottish consciousness and there followed a campaign to stop the local Howden's engineering works either knocking it down or turning it into an apprentices' school.
Both men remember a strict school regime, dominated by rote learning and discipline.
Mr Sewell, who spent most of his career in steel distribution and now works as a messenger at The Herald newspaper, recalls knitting squares which a teacher and sewing them into a blanket as part of the war effort.
His strongest memory is of his evacuation on September 2, 1939, carrying his gas mask in a bag, the day before war was declared, to Mauchline in Ayrshire. He and his older brother were to remain there for little more than a year, their stay cut short because they were being under-fed by their host family.
Back in Glasgow, there were nights, especially during the Blitz on Clydebank, when Stan hunkered down with his family in the shelter owned by Howden's, where only company workers and their families were allowed to shelter. In the mornings, children would pray that the all clear siren would sound too late for them to go to school.
From his desk at Scotland Street School, Stan could look out the window to the air raid warden's shelter behind the school. Some of Stan's education during the war years was at nearby schools, as the war led to a shortage of teachers and, with many children evacuated, a fall in pupil numbers.
Discipline was maintained by regular use of the tawse. "I was always a scaredy wee cat, but some of the boys really went to town. They were really cheeky," says Mr Sewell.
Were his school days happy ones? "Yes, I think so. You were mainly unhappy if you had not got your sums right. I used to worry about getting the belt for not doing my homework right."
Ten years later, when 5-year-old Gus Macdonald entered the school, the disciplinary regime had changed little and families were living in post-war austerity.
"We still had rationing. In the school there were very few frills. I don't remember any extra-curricular activity," he says.
Stan Sewell and Lord Macdonald are among a number of former pupils and teachers taking part in Stories from Scotland Street's Archives, an exhibition of photographs and memories from May 5 to June 11.