Brenda Ann Spencer was born on April 3, 1962, in San Diego, California. She was the youngest of three children in her family. Her parents, Dorothy Nadine and Wallace Edward Spencer, got married on December 12, 1954. However, their marriage faced difficulties when Brenda's mother discovered that her husband was unfaithful. This led Dorothy to file for divorce in January 1972.

After the divorce, Brenda lived with her father in a neglectful environment. They often slept on a mattress on the living room floor. The home was messy, filled with empty bottles of alcohol. Brenda later claimed that she experienced total neglect from her mother and alleged sexual abuse from her father. However, her parents disputed these claims.

Brenda lived directly across from Grover Cleveland Elementary School. During her childhood, she often showed signs of distress and disconnection. She attended Patrick Henry High School but struggled academically, showing little interest in her studies. One of her teachers often asked her if she was awake during class. Despite this, she had a talent for photography and won an award in a competition hosted by the Humane Society.

As a teenager, she became increasingly troubled. In early 1978, she was referred to a facility for students with behavioral problems due to her truancy. Staff members there alerted her parents that she was showing suicidal tendencies. That summer, she was arrested for shooting out the windows of the school with a BB gun, as well as for burglary.

In December of that same year, a psychiatric evaluation suggested that Brenda should be admitted to a mental hospital for depression. However, her father refused to allow this. For Christmas 1978, he gave her a .22 caliber rifle and ammunition, a choice that Brenda later remarked upon with sadness, saying she had asked for a radio instead.

Brenda would often express violent thoughts and had a particular hostility towards police officers. She described herself as a "radical" and often proclaimed her disdain for law enforcement, which caused many of her classmates to feel frightened around her. A bicycle accident had left her with an injury to her brain, but she continued to exhibit troubling behavior that concerned those around her.

On January 29, 1979, Brenda Ann Spencer, a 16-year-old girl, began shooting from her home across the street from Grover Cleveland Elementary School in San Diego. She shot at children waiting for the school gates to open. The first victim was nine-year-old Cam Miller, who was wearing blue, a color Spencer liked. She continued shooting as Principal Burton Wragg and teacher Daryl Barnes attempted to help the children. During the attack, Spencer killed Principal Wragg and 56-year-old custodian Mike Suchar, who was trying to pull a student to safety. Additionally, she injured eight children and a police officer named Robert Robb, who was shot in the neck when he arrived to assist.

After firing thirty-six shots, Spencer barricaded herself in her house for several hours. A reporter managed to contact her by phone while she was inside. During the call, she stated she had shot at the children and adults because she did not like Mondays and claimed it made her day more exciting. She also told police negotiators that the people she shot were easy targets and indicated she would come out shooting. Eventually, she exited her home after police promised her a meal from Burger King.

Brenda Spencer was later charged with murder and assault with a deadly weapon. She pleaded guilty to two counts of murder and received a sentence of 25 years to life in prison. Her case is often noted as one of the first modern school shootings in the United States.