ANAHEIM, Calif. — A Southern California high school canceled an annual dress-up day for seniors, saying that students who dressed as gang members, a US ­Border Patrol agent, and a pregnant woman pushing a stroller demeaned Latinos.

The June ‘‘Seniores and Senoritas’’ day at Canyon High School in Anaheim prompted complaints by two former students and an investigation by the Orange Unified School District.

The event, held for at least the last three years, was approved by campus administrators and they have been ordered to undergo diversity and sensitivity training, the Los Angeles Times reported.

‘‘We are serious in our intent to provide effective action so that this will not recur,’’ Aileen M. Sterling, the district’s executive director of secondary education, wrote in an Aug. 10 letter summarizing the investigation.

School administrators failed to tell students how to dress and were held responsible even though they immediately ordered students to take off the gang garb.

‘‘Even if strict guidelines were provided, the result would still lead to hurtful and demeaning messages about the Mexican culture and to the students of the Mexican, Hispanic, and Latino descent,’’ Sterling wrote.