The 1970s and 1980s weren't particularly strong decades for St. John the Evangelist. The school still lacked a gymnasium, a library, a science lab, fine arts and technology programs, and the grades of Pre-K and Kindergarten. By this point, the school also no longer had football or cheer teams. These challenges reflected broader difficulties within the archdiocesan school system: while the archdiocese operated several primary schools, St. Pius X — the sole high school intended to receive their graduates — had capacity for only about 500 students. For St. John the Evangelist students in particular, traffic congestion made the commute to St. Pius X especially difficult.

The archdiocese initially drafted plans to build several new high schools, one of which was intended to be located near St. John the Evangelist. Those plans were ultimately abandoned; instead, the decision was made to significantly expand St. Pius X, tripling the size of its campus.

At the same time, St. John the Evangelist began receiving funding to address many of its longstanding deficiencies. During the 1980s, air conditioning was finally installed throughout the campus. In the following decade, the school added a gymnasium, an art studio, a library, and new computer and science laboratories. The church also expanded, which allowed the school to introduce Pre-K, Kindergarten, and music classrooms. Asbestos, mercury, and lead — which were hazardous materials found in ceilings, carpeting, and tiling — were largely extracted from the campus to further improve student safety. The school adopted the blue, gold, and white color palette used today, replacing the original red and white, and updated its uniforms to the design still in use.

Meanwhile, highway expansion projects effectively doubled the capacity of the interstate system, essentially removing the traffic barriers that had made travel to St. Pius X difficult. In 1997, St. John the Evangelist received its first National Blue Ribbon School of Excellence award and was one of the first archdiocesan schools to receive this honor.

This period of development brought renewed stability to both the school and the wider archdiocesan system.

Concern for school safety was minimal during this period, as was common across the United States in general. As seen in photographs from the time, St. John the Evangelist, like every other archdiocesan school, did not have perimeter fencing. Schools generally relied on students to remain on campus and assumed that outsiders would not attempt to enter. During the 1970s, some archdiocesan schools even adopted an open-campus model, allowing students to leave during lunch periods or other non-instructional time; St. John the Evangelist may have operated under similar practices.

Dismissal procedures were similarly informal. When the final bell rang, students were often free to linger on the grounds, socialize, or walk around the campus. There was no structured dismissal procedure, and students typically located their parents on their own. It was common to see children crossing parking areas and nearby streets independently. Organized student safety patrols and the current carline system had not yet been established.

In some areas, these looser policies gave students an early preview of the independence they would later experience in high school.