Mr. Dillard McCollum was selected to succeed the previous superintendent after he resigned in July 1942. Mr. McCollum had first been associated with Harlandale as a student at Morrill School. He served the district for 37 years as a teacher, principal, and superintendent. Mr. McCollum passed away June 8, 1962 while serving as superintendent of HISD. The new high school was named Dillard McCollum High School in his honor. 

In 1968, the citizens of Harlandale passed a $5,000,000 bond issue that provided funds for, among other things, a new ROTC complex, enlarging the gym, expanding its cafeteria, and adding air-conditioning to the library.  

In October of 1971, the National Bellamy Award was presented to McCollum High School as the representative of Texas public schools.

In December of 2004, the decision was made to permanently fill-in and cover up the McCollum High School swimming pool. 

In June of 2012, there was a ribbon-cutting ceremony for band halls and field houses at Harlandale High School and McCollum High School. 

In August of 2015, there were ribbon-cutting ceremonies for a new Health Science Technology building and an Automotive Technology Building at McCollum High School.