Mother Teresa, a Catholic nun who devoted her life to helping India's poor, has been declared a saint in a canonization Mass held by Pope Francis in the Vatican.
The school, located at the foot of Convent Road beside a poorest of poor locality of Entally slum, is the same institution where Mother Teresa taught geography and catechism (classes on Christianity for Catholics) from 1932 and could glimpse the world of poverty outside the school from her classroom window.
The Macedonian born nun served for a time in west Belfast during her life. It was nevertheless the highlight of Francis' Holy Year of Mercy and quite possibly one of the defining moments of his mercy-focused papacy.
"Pope Francis, Pope John Paul II and Mother Teresa are the church figures I admire and love most and in some way all three are here today", O'Brien said.
Setting controversy aside, what does this formal rite of canonization mean for her title - do we now call her "Saint Teresa?".
The canonization Mass will begin with hymns and proceed nearly immediately to the rite of canonization: the declaration that Mother Teresa is now a saint. "She made her voice heard before the powers of this world, so that they might recognize their guilt for the crime of poverty they created".
She ceaselessly proclaimed that the unborn are the weakest, he said.
Most of the Catholic Church's saints or blessed people are honored decades, if not centuries, after their deaths.
The Norwegian Nobel Committee said her spirit and the respect she had for the worth and dignity of human beings inspired constructive efforts to do away with hunger and poverty.
In Shillong, the Festival opened with the Film "Mother Teresa and Me" made by noted Photographer and Film Maker Gautam Lewis who was raised by Mother Teresa after his parents abandoned him while he was a young infant in Kolkata. "With great spontaneity, I think we will continue to call her Mother Teresa", he said.
Francis has never publicly mentioned this "darkness", but he has in many ways modeled his papacy on Teresa and her simple lifestyle and selfless service to the poor: He eschewed the Apostolic Palace for a hotel room, made welcoming migrants and the poor a hallmark and has fiercely denounced today's "throwaway" culture that discards the unborn, the sick and the elderly easily.
Many here were so excited they couldn't wait till mass to celebrate.
But on Sunday, he admitted that even he would find it hard to call her "St. Teresa", since her tenderness was so maternal.
She expired in 1997 and was set on a fast track for sainthood shortly afterwards.
Cheering the pontiff in Saturday's crowd were many nuns from her Missionaries of Charity order, each wearing the characteristic white sari trimmed in blue that makes them easily identifiable worldwide where they care for the needy.
The ceremony came a day before the 19th anniversary of Mother Teresa's death in Kolkata, the Indian city where she spent almost four decades working in wretched slums.
Throughout the night, pilgrims prayed at vigils in area churches and flocked before dawn to the Vatican under heavy security to try to get a good spot for the Mass that was expected to draw more than 100,000 people.