In 2014, he won a special election to succeed Marguerite LaMotte on the Los Angeles Unified School District Board of Education after she died, serving until he announced his retirement in 2024.

He furthered his education by attending Loyola Law School, where he was awarded a teaching fellowship and earned a master's degree in mathematics.

[3] In 1979, McKenna assumed the role of principal at Washington High School in Westmont, California, which faced challenges with low academic performance, frequent student absences, and gang violence.

Throughout his tenure as principal, he successfully reformed the school to a point where nearly eighty percent of its graduates pursued higher education.

[11][12] Some of the members of the Board of Education called his actions arrogant, blaming him for deficits that the districts was facing at the time, and he lost a no-confidence vote.

[16] On December 5, 2013, longtime Los Angeles Unified School District board member Marguerite Poindexter LaMotte died, with supporters rallying around McKenna to be appointed to her seat.

[19] In the primary election, McKenna and education policy advisor Alex Johnson emerged as the top two candidates, advancing to the runoff.

In September 2019, McKenna helped to launch the Los Angeles County Metropolitan Transportation Authority pass program for K-12 students in the LAUSD.