Assumption Catholic School was built on the five acres obtained by Msgr. John Limmer in 1923. It consisted of a brick exterior and wooden framing on the inside and housed ten classrooms and an auditorium. Religious services were held in the auditorium in the fall of 1923 and classes for first through eighth grade began in the fall of 1925 after the Benedictine sisters moved into their new convent.

Assumption School faced severe overcrowding in the 1950's under Msgr. Patrick Byrnes.
The 10 original classrooms were insufficient for the 470 pupils enrolled, let alone including new registrants. To correct this situation, two classrooms were made out of the ladies clubrooms on the first floor. Contractors built a new kitchen and converted the old kitchen into a library.

In the summer of 1955, Msgr. Byrnes introduced further improvements. At the time, school enrollment had increased to 517 and classroom space remained insufficient. The Knights of Columbus quarters were converted into two classrooms.

In 1959, St. Leo's parish and school were created in the southern part of Hibbing. The school helped relieve some of the congestion experienced at the Assumption Hall in first through sixth grade. The school opened in 1961 with first and second grade with plans for adding one class per year.

In 1971 Assumption School discontinued the 7th and 8th grades after the Lincoln School consolidated all the 7th and 8th grades in Hibbing Public Schools. As Hibbing population growth waned, enrollment declined at Assumption to 150 by 1984. As the number of available teaching sisters declined, lay teachers increased in number and importance.

In 1994, the diocese first broached the subject of a Hibbing-wide consolidation. In 1998, the St. Leo's and Assumption Schools and churches were merged under one pastor, principal and school board. Kindergarten expanded to a five full day schedule. A Pre-K program was added along with a year-round school-age child-care program. New playground equipment and a state-of the art computer lab were added to the school to enhance the school's environment.

The two schools consolidated into one building at the Assumption School location in the fall of 2003. Assumption School celebrated 80 years of  providing Catholic education during the 2005- 2006 school year by holding an All Catholic School Reunion in June, 2006. A ground breaking ceremony was held during the Reunion and marked the beginning of construction of Phase I of the Becoming One Campaign. The staff and students began the 2007-2008 school year in the new wing. Parish staff moved into the former Assumption School, which coincided with the sale of the St. Leo's Rectory. The remodeling of the former school began in January, 2008 and allowed all the school programming to be relocated to the first floor at the beginning of the 2008-2009 school year.