Kidd was described by former teachers and classmates at Everest Middle School as quiet and defensive. Kidd reportedly often avoided eye contact and refused to speak. In seventh grade, Kidd was reported to the Everest Middle School counselor by a teacher, who then alerted Kidd's parents, after noticing self inflicted cuts on Kidd's arms. This led Jane Kidd to have Ghost evaluated by a psychologist and to enroll them in therapy. Kidd was diagnosed with autism and clinical depression at the age of twelve. Kidd reportedly did not object to treatments such as medication and therapy. Ghost's father, John Kidd, began taking Ghost on trips to shooting ranges in the belief that recreational use of firearms would help aleviate stress and self-harm urges. Journal pages and online posts written by Kidd at this time show the beginning of an interest in firearms and various mass murderers.

In their highschool years, Kidd's struggles with mental health seemingly worsened. Students who attended class with Kidd reported that Kidd would frequently act rudely or even threaten their peers. Their freshman year, Kidd was subjected to a meeting with the Terence High School principal to discuss a statement they made in which they threatened homicide to an unnamed classmate. School staff involved with handling this incident later claimed that the matter was not given further punishment due to Kidd's history of mental illness and maladjustment, which is something the administration has stated to regret. Various accounts from students admit to mocking Kidd in private due to their abnormal behavior, though all accounts claim that no prominant bullying towards Ghost took place. Kidd's teachers claimed that their already struggling attendance and grades took an even greater toll in the months following the end of Kidd's junior year, leading to Kidd repeating the grade; this setback was later mentioned in Kidd's writing to be a motivation for the massacre. Despite multiple reported attempts from classmates, Kidd refused most social interaction and did not talk to or see other students outside of school. One exception was made, though, as Kidd celebrated their seventeenth birthday with Stem Lemieux and Promise Smith at the Kidd family home in Oregon.

Coherent plans for an attack did not appear in Kidd's writings until the summer before the incident, though an idealization of becoming a mass murderer was first mentioned by Kidd as early as eighth grade. Kidd was seemingly interested in the prospect of being a notorious figure, as well as committing suicide in an extreme manner.