The teacher's recollections will add to speculation about Mr Obama's links to Islam during his much-anticipated visit to Indonesia, the world's most populous Muslim nation, as part of his ten-day tour of Asia.
His middle name, Hussein, and the fact that his stepfather was a Muslim, have combined to perpetuate rumours about Mr Obama's religious leanings. The number of Americans who think that he is a Muslim has grown since his inauguration to one in five.
Mr Obama moved to Indonesia with his mother and Indonesian stepfather, Lolo Soetoro, when he was 6, and lived there for four years. In his memoirs he recalled his time in the country as the "bounty of a young man's life" and there is affection and pride among Indonesians for the boy who ended up as President of the United States.
The teacher, Effendi, who taught at Menteng One for 29 years, remembers Mr Obama as a "fat, curly-haired, curious boy". The school had an international mix of pupils, including Christians, Hindus, Buddhists and Muslims.
Mr Obama attended classes on Islam while the Christians attended classes on Christianity, said Effendi. Barry, he said, was alone among the pupils in that he insisted on attending both.
"His mother did not like him learning Islam, although his father was a Muslim. Sometimes she came to the school; she was angry with the religious teacher and said 'Why did you teach him the Koran?'" said Effendi.
"But he kept going to the classes because he was interested in Islam. He would also join the other pupils for Muslim prayers."
Questions over Mr Obama's religion were fuelled, in part, by comments about his Muslim roots made by Hillary Clinton during the Democratic party leadership campaign.
The conservative American media took the speculation further by claiming that Mr Obama attended a madrassa - Islamic school - as a child. Mr Obama's former classmates, however, have dismissed the claims as nonsense.
The US President - who has cancelled a scheduled trip to Indonesia twice before - may be stymied again by air traffic disruption caused by an ash cloud emitted from Mount Merapi.
The volcano has been erupting since October 26, killing at least 117 people.
Mr Obama is due to arrive in Jakarta tomorrow after three days in India.
A third cancellation would not be welcomed in Indonesia, where some offence has already been taken at the brevity of the visit.
The homecoming anticipated so keenly by Indonesians has been reduced to less than 24 hours; the shortest amount of time he will spend in any country on the Asia itinerary.
Pupils at Menteng One, who have been rehearsing songs and dances for more than a year, will be particularly disappointed.
Their headmistress has not yet had the heart to tell them that Mr Obama will not, after all, visit their school.
"When I told them in March that he had cancelled his trip again some of the children cried and asked why?" HJ Hasimah said. "I don't know what I will tell them this time."