In 1857, four years before the Civil War began, the mission church of the Assumption of the Blessed Virgin Mary was organized. The entire area was wooded and small farm houses were the only buildings in existence. Mass was celebrated in the home of James Morrow. In 1863, a lot and small house were purchased for $500, and the house was remodeled at the corner of the present Royalton Road and Ridge Road in what is now North Royalton. A year later, a parcel of land was remodeled into a church. This building served as the church for the next forty-one years until 1905. As the population of the area grew, the present property on Broadview Road was purchased in 1929. In 1930, a stone-trimmed brick church seating 325 persons was built. This served the people for the next 40 years. In 1938, the parish had grown to 100 families.
The Ursuline Sisters from Cleveland taught CCD classes in the church building on weekends, and in 1957 an eleven-classroom school was built. The Sisters of the Incarnate Word, from Parma Heights, were invited to staff it. Sr. Agnes (formerly Bernadette Kane, SIW) was the first principal to lead the staff of five sisters and four lay teachers. They staffed eight grades in eight of the ten classrooms. Approximately 375 students were enrolled in the first year. There was a steady increase in enrollment for ten years, peaking at 532 students in 1966. At this time, eleven classrooms were utilized with one being the large space on the lower floor. For the next four years, the number of students decreased gradually so tuition was initiated in 1967.
A library was established in the same year the school opened. From a minimum of fiction and reference books, the holdings of the library increased year by year to include books and audio-visual materials in all subjects. This was all funded by the school. The library was originally a small room on the main floor. It is currently in the lower level of the original school building. The library has been computerized since 1997. In 1999, walls were constructed, making the library a large defined room. Accelerated Reading was added to the library program in 2000. In 2003, the school added the most current method of technological integration by being awarded a Numonics Board (interactive whiteboard) with monies from a grant. Accelerated Reader began in the 2007 – 2008 school year.
The school created a Computer Lab for student instruction in 1987. In 2000, the Macintosh Computers in the Lab were moved to the primary grades and a state-of-the-art Technology Lab was formed with the purchased of Dell Computers and Microsoft Office Professional. Currently, all classroom teachers have computers on their desks for access to a grading program, online communication with parents and students, and to assist in the integration of technology into the curriculum.
In 2014, the computers in the Computer Lab were replaced with 32 Windows 8 computers. The previous Windows 7 computers were distributed throughout the school classrooms and library.
A school addition in the summer of 2002 allowed for smaller class sizes, with a ratio of 1:21 instead of 1:32. The original building became the primary wing, for grades Kindergarten through Grade 3, with two classes of each grade. Some classrooms were reconstructed to become the Clinic, Art Room, and a Conference/Teacher Assistant Room. The new side of the building became the Middle School, for grades 5 – 8 on the lower level and grade 4 and Science Lab on the top level. A Preschool was opened in 2005, providing early education for 3 and 4 year olds and Pre K students. It is housed in the new building. Also included in the new building are a Music Room, a Science Lab, and a Cafeteria, which provides the National Hot Lunch Program for students. All grades include ActivPanels, a computerized whiteboard, for instruction.
The school name was changed to Assumption Academy after the school renewed its Accreditation in May 10, 2010 from the OCSAA (Ohio Catholic School Accrediting Association).