On April 24, 1865, Mother Theresa wrote the Holy Father saying that we, the School Sisters of Notre Dame “prostrate  at the throne of your Holiness, beg for the final approbation of ” the holy Rule which had been granted tentative approval for six years required test period in 1859.   On August 28, 1865, in a Circular, Mother Theresa was able to announce that the Rule had received final approval. That year the congregation taught 50,000 students thus having evidence of their ability to survive.

The Holy Rule was first printed in 1860.