Milby began its life in March 1926, replacing the former Harrisburg High School, which was located several blocks south of Milby. Thirteen teachers and 212 students formed Milby's initial population. The $180,000 campus had, and still has, a
Romanesque exterior. Milby has since had various expansions and renovations. Originally a predominately non-Hispanic White school, Milby became mostly Hispanic as the population of the
East End area increased. Prior to 1965,
Milby admitted White and Hispanic students, while it did not admit Black students. At the time, Hispanics were considered white. Houston high schools
desegregated one grade per year from 1965 - 1967. Milby High School was used as a filming location for
My Best Friend Is a Vampire in 1986; it was renamed "Milton High School" in the movie. Many interior scenes, including scenes of the main character in his bedroom, were filmed inside the school, and the exterior was used in the movie as well. Students at Milby were extras in many scenes, as the filming took place during school hours. After the movie was completed, the sign on the exterior of the school that had been in disrepair was replaced with a new one by the production company. In September 1991, Milby was one of 32 HISD schools that had capped enrollments; in other words, the school was filled to capacity and excess students had to attend other schools. On November 14, 1991, 18-year-old Francisco Contreras received four gunshot wounds in his feet and leg outside of the cafeteria at Milby. Police arrested a 16-year-old described by HISD officials as a "disturbed freshman." In December 1991, Milby was one of the largest high schools in Texas, with 3,617 students. Due to the overcrowding, by that month Houston ISD trustees approved a plan to open a new high school in September 1995 instead of in 1997. Milby, in the meantime, had already had additions, so the district did not need to install very many temporary buildings. By 1997 the new high school had not yet been constructed; area community leaders and parents anticipated the construction of
César Chávez High School, as Austin and Milby were still overcrowded. Prior to 1997, residents zoned to Furr also had the option to attend Austin and Milby high schools; in 1997 the school district canceled the option. In the fall of 2000, Chávez opened and took most of Milby's traditional neighborhoods. In turn Milby absorbed some students from Austin. Areas that were zoned to Milby in 1998 were rezoned to Chávez. In turn Milby absorbed attendance areas from
Austin and
Furr high schools. In 2007,
Johns Hopkins University referred to Milby as a "dropout factory," where at least 40 percent of the entering freshman class does not make it to their senior year. During that year, 20 percent of high schoolers zoned to Milby chose to attend a different Houston ISD school. A petroleum academy opened in Milby in the fall of 2008.
Halliburton donated $27 million to provide engineering and geoscience software while
Shell Oil Company donated laptops altogether worth $115,000. The first petroleum academy class graduated in 2011. Around 2014, the school began digitizing its old yearbooks. As of August 2014, the Milby campus closed for reconstruction. The school administration and the 9th grade students were temporarily housed in trailers at Attucks Middle School in
Sunnyside, while students in grades 10-12 were housed at
Jones Futures Academy in
South Park. On December 18, 2014, groundbreaking for a new campus occurred. The project comes from the 2012 bond. The original 1926 building, made of concrete and brick, will remain, while other portions have been demolished and replaced with new construction. ==Student population==