[10][11][8] The new building had its cornerstone laid at ceremonies held in December 1912;[12] it was completed in April 1913, with a facade oriented towards Christie Heights Street near Broad Avenue.

[16]) A trolley line ran along Broad Avenue at the time and this enabled students from outside Leonia to reach the high school in a convenient manner.

[11] An addition was built onto the east side of the school in 1917, that featured a larger facade which was oriented directly onto Broad Avenue.

[19][22] In 1945, the Board of Education proposed the addition of a new gymnasium that would cost $275,000 (equivalent to $4.7 million in 2023)[23] and would be made available to town residents for outside recreation activities.

[8] (The Board sought public support for the project by describing it as a war memorial that would of "practical benefit" to veterans and their families.

[27] As part of replacing the tuition income from these two towns, Leonia High School began receiving students from Edgewater again in 1958,[26] a relationship that continues to this day.

[29] Completed in 1963, the expansion consisted of a new wing on the southeast corner,[8] one that housed the enlarged school library and several classrooms.

[30] There were many problems: the shared, cramped student lockers; a small auditorium; inadequate laboratory space for sciences; and useless time being spent in study halls.

[34] Nevertheless, efforts to improve the level of academics carried on; from the early days, the faculty of Leonia High School often had connections to Teachers College at Columbia University,[17] and the district was part of the Columbia University Teacher's College Metropolitan School Study Council, which provided the faculty with various research materials.

[30] Feelers were put out to a number of surrounding towns during 1968,[30] and discussions with one, Bogota, encompassing full K–12 regionalization, became quite serious and were the subject of assessment reports and public meetings.

[34] In one publicized case, a 150-square-foot (14 m2) windowless, poorly ventilated room in the basement, with student desks crammed together, was being used daily for five classes in mathematics and other subjects.

[34] Undeterred, the Board of Education put the exact same proposal up for another vote in September 1972, hoping to sway enough minds to get approval.

[42] By then, many Bergen County municipalities were rejecting referendums designed to overhaul or replace aging infrastructure, with inflation of that era being an overriding economic concern.

[42] Nonetheless, put up for a vote in October 1974, the referendum passed, a result that The Record called "all the more surprising following bitter dissension this fall among a number of factions involved in the school issue.

[7] But the demographics of Leonia changed over time, with a large number of Korean American families and businesses moving into town.

[45] Moreover, the demographics of Edgewater were rapidly changing; formerly a town populated by factory workers that had a rough-and-tumble reputation, the local industries were being replaced by expensive condominiums filled with executives and other white-collar types working across the river in Manhattan.

[50] During 2009 and 2010, the high school building had its entire roof replaced, its HVAC system redone, and solar panels added.

[45] The college-preparatory academy was part of a trend of old-fashioned home economics programs being updated to account for increased student interest due to competitive cooking shows on television.

[55] These academies grouped interested students in smaller cohorts in order to pursue potential career paths in combination with specific experience outside the classroom environment.

[56] By the 2020s, Leonia High School would also offer academies in mathematics and science, business, humanities, music and arts, and vocational trades.

[23] In 1953, the accreditation report gave Leonia High School a positive assessment, praising the students, the teachers and other staff, and the overall cooperative atmosphere, and noting the low rate of drop-outs.

In January 1966, for instance, the team placed a close second to The Wheatley School of Old Westbury, New York on the television show It's Academic.

[70][71][72] Prior to the realignment that took effect in the fall of 2010, Leonia was a member of the Bergen County Scholastic League Olympic Division.

[77] The 1967 boys basketball team, led by longtime coach Lee Clark, used its height to its advantage and defeated Burlington Township High School by a score of 73-65 in the Group I tournament final to finish the season with a record of 20–4.

[84] Leonia football, which is a co-op program with Palisades Park High School, became the first cooperative program to have reached a finals game in state history when the team made the North Jersey II Group III state championship game in 2012, falling to Summit High School by a 30–0 final score.