Jelley (91), the coach of 1976 Olympic 1500m champion Sir John Walker, was a pupil at the school from 1927 to 1935.
It was the first time he had visited his old school since the 125th anniversary 24 years ago, and it was the first time he had been there during school hours since he was a pupil in 1935.
He spoke to the school assembly and then visited some classrooms.
''The children were positive and very friendly,'' Jelley said. Mornington School pupils wear a scarlet jersey as their uniform today.
''We didn't have a uniform in my day but we had a school tie,'' Jelley recalled.
''It was in the same red, yellow and black colours as the Zingari-Richmond rugby club.''
Jelley was in Dunedin to celebrate the 90th birthday of his sister, Mary Jamieson, tomorrow, and was asked to visit his old school by principal Brent Caldwell.
''It was a great opportunity to come to the school, especially when all my brothers and sisters were also pupils there,'' Jelley said.
He addressed the school assembly in the old gymnasium, the only building left from his own days as a pupil.
''I remember playing bull rush on an old rough paddock. We lived a kilometre from the school and at lunchtime we ran down Galloway St, had lunch, and then ran back up to school. It was good training.''
The Jelley family were all pupils at Mornington School and will attend the 150th jubilee at Labour Weekend next year. The other siblings are Charley (93), Stan (87) and Effie Cockburn (80).
Arch Jelley was a talented runner. He came fourth in the New Zealand senior cross-country in 1948 and was a member of Otago and West Coast (North Island) winning teams.
Stan won a bronze medal for Otago at the New Zealand cross-country, Charlie was a competitive cyclist, Effie was talented at track and field and Mary has won six Bowls Dunedin titles.
An earlier generation of the family also attended Mornington School. Father Albie, the local barber, was a first-class cricket umpire and officiated in the first test between the West Indies and New Zealand at Carisbrook in 1957.
Arch Jelley, a former schoolteacher, was principal of Sunnybrae Normal School in Auckland when he retired in 1987.
''On the day I retired I flew out to the world track and field championships in Rome,'' Jelley recalled.
Walker, the first runner to break the 3min 50sec barrier for the mile when he ran 3min 49.4sec in 1975, was Jelley's best athlete.
He coached more than 10 internationals. The one athlete he coaches today is New Zealand 1500m champion Hamish Carson (Wellington), who is close to the Commonwealth Games qualifying time for Glasgow.
