She had travelled by train with the slightly older Sister Alphonsa Jones, who was to be her boss and companion for the next five years. Together they were to be the founding nuns of St Michael's Catholic Parish Primary School.

Sister Thecla was 24, and even in her dark brown, heavy habit, in the height of summer, you could tell she was an attractive woman.

There was a kindness in her eyes and smile. Even long after her looks had faded and her habit had been replaced with more comfortable civilian clothing, at almost 100 years old she was still a striking woman.

The nuns arrived in Thirroul two weeks before the start of the new teaching year in 1940 and were shocked to discover there was no school building, no teaching resources and no convent in which to live.

There was also no warm welcome from the parish priest. While the northern suburbs Catholic community had rallied support for a new school, it appears Father John O'Farrell may have been less than enthusiastic about having two females in his realm.

On January 28 he announced to his congregation that classes would begin inside the church for kindergarten to year 3 students. Older Catholic children would have to remain at the nearby Thirroul Public School or travel by train or bus to St Joseph's Convent School at Bulli.

"To our horror there was no school, but we were informed that we would teach in the church," wrote Sister Thecla just before her oak jubilee in 2014. "We were given a quarter of the church with two blackboards on easels. That was the extent of the school's equipment."

With no resources or money provided by the parish, Sisters Thecla and Alphonsa caught the train back to Sydney to purchase the basics with the £5 they had been given by their superior, Sister Marcellinus. The money stretched to buy chalk, dusters and a few textbooks.

On their return they met with the school's 34 new students. The first intake lined up and stood tall against the outside northern wall of the church, eager to meet their new teachers.

Pat Cadogan (nee Agnew) recalls that everyone was excited.

"I remember the day we enrolled," says Pat. "The nuns asked what year we were in. I put myself up a grade. Gave myself a bit of a promotion. They realised later and amended the error. But it was an exciting time. Our parents all wanted us to have a Catholic education. It was important to them."

Inside the church a curtain was put up to divide the altar from the students and the pews were pushed aside to make way for desks. The "neatly kept" blackboards were the only division between the classes.

"The nuns battled on under trying conditions," explains Ron Tuckerman, a student from the first intake. "In the beginning they had to go out and solicit donations to buy chalk."

Another student, Arthur Martin, remembers that on the first day of the new school Father O'Farrell was reluctant to hand over the keys to the church.

"I remember we were all lined up on the first day outside the church waiting for the nuns to get the keys. Eventually they did but I think it would be fair to say that the parish priest didn't want the nuns in his church, at least to begin with," says Arthur.

With not much room in the school grounds, Sister Thecla would walk her pupils to a nearby empty paddock to play rounders. Rolling up the sleeves of her habit she would join in the game using a fence picket as a bat.

"She loved it. She was very active and could really whack the ball," says Ron. "She would roll up the sleeves to the elbows and run. Everyone always wanted to be on her side."

During the war, air raid shelters were dug in the paddock and the nuns would plant religious medals and sprinkle holy water in there each Friday to protect their charges in the event of an enemy invasion.

Also, at the end of each week, as a treat, Sister Thecla would share with them Australian stories like Blinky Bill and We of the Never Never.

"Sister Thecla was fantastic. We were all in love with her," adds Arthur. "She was just so kind to everybody. Sister Alphonsa was the school principal and a bit more serious."

By the end of the year more than 90 students had enrolled at St Michael's.

"The school was quite primitive," says Sister Tess, a Josephite nun and Sister Thecla's niece. "It was a stark contrast to the beautifully built public school across the road. The irony of it was that the students came in droves to this poor little school with no proper facilities. I think the two nuns must have had some kind of charisma for that to have happened."

While a cottage had been purchased near the church for a convent in 1927, the nuns did not move in until 1950. The parish rented it out to tenants. The nuns were forced to travel each day from the Sisters of St Joseph's Bulli convent, which was a hardship for them.

Around mid-year Father O'Farrell was replaced by Father James Mullin.

"Initially the nuns believed that Father Mullin didn't support them," explains Ron. "But he had been left with a difficult financial situation. When he arrived he had to replace furnishings in the presbytery. He was also left with a huge debt from the extensions to the church in 1939. So in the early years he was limited in how much he could support the nuns. They were tough times. But it didn't dampen the enthusiasm to start the school, and everyone wanted to see it succeed."

The parish had attempted to buy land near the church to build the school but the Protestant owners refused to sell. In the end hotelier and entrepreneur Johanna Ryan came to the rescue, purchasing the land. She immediately handed it over to the parish with the provision that a Catholic school be built within 10 years of her death (a new school building was constructed in 1951).

Mrs Ryan also provided a little stove for the nuns so they could cook their lunch in the sacristy and kept them in bread each day. A Catholic butcher in Thirroul donated meat.

Each Friday the nuns would send one of their students, Tony Bolt, who later became a priest, to pick up fish and chips for their lunch. They often shared what was left with those students who would help clean up the church at lunchtime or after school.

"There was just the one learning area at the back quarter of the church," remembers Father Tony Bolt. "We did not see anything strange about this crowding. The nuns managed crowd control very effectively. Noise was not a problem. The teachers were very much in charge."

At the time Australia was a sectarian society divided between Catholics and Protestants. Mixed marriages were frowned upon and in some cases family members were disinherited.

Catholics stuck together and the church and school community became the focus of life.

Father Bolt says there was a sense that Catholics were the underdogs, with government funding for education going to public schools.

"We did not feel badly done by because the results in bursaries and scholarships came more frequently to us," he says. "The dedication and interest of the sisters made all the difference."

In the '40s and '50s life in the convent was strict.

As she grew as a teacher, Sister Thecla would always be an advocate for fair play and justice, but she could also be daunting and forthright, says Sister Tess. She had a shadow side and was exacting about the proper way to do things.

"She had a strict code, a stern exterior and a heart of gold," says Sister Tess.

Sister June Bath was also a student in the church in those early years.

"I remember my first day of kindergarten in the church," she says. "I had Sister Alphonsa. I was five. She was very gentle and kind to us."

Sister June was in year 6 when she decided to become a Josephite nun. She was 13 when she was sent to boarding school at Hunters Hill to begin her training as a nun.

"My father didn't want me to go. I know I was young but you've got to do what God wants you to do," she says. She became a postulant after her Leaving Certificate.

"I liked the spirit of the Josephites. I had grown up with them. The nuns impressed me with the simple way they lived. The fact that they cared about people. That was the main thing. I liked how they didn't put themselves above other people. It's an Australian order, for the Australian people."

Sister June returned to St Michael's in 1979 to teach year 2 for a year.

"I was pleased to be closer to my family [who lived at Austinmer]," she says. "But it was strange being at the school. When I walked into the classroom I could tell I had been to school with the parents of some of my students. I recognised them straight away."

Both current and former students and staff have spent a week marking the 75th anniversary of St Michael's Catholic Parish Primary School. The celebrations coincide with the Feast Day of St Mary of the Cross MacKillop, the founder of the Order of the Sisters of St Joseph.