Some students were escorted from the building to the main entrance to meet their families, who were warned to exercise patience to ensure everyone's safety.
Wilcox said there were many "young people who witnessed this tragedy..."
Police said they were investigating the shooting, but were convinced that it was an isolated incident.
Dozens of parents gathered outside of the school of about 2,000 students.
Anxious parents and carers rushed to the school after news of the shooting broke, with parents initially told they could come to pick up their kids from 8:50am EDT.
Several of the departing students said they learned about the incident from Instagram.
Charlotte-Mecklenburg Schools issued a statement saying the student was shot Monday morning at Butler High School in Matthews.
The shooting occurred shortly before 7 a.m., and a school resource officer was nearby, when it happened, Wilcox said a press conference. Students remained inside with the school on lockdown for about two hours after the shooting.
A student opened fire at Butler High School on Monday, striking a classmate, police said. Classes will proceed on campus today for students remaining on campus. Simpson also told the newspaper that he made his son, who is in the ninth grade, "sneak out a back door".
"[CMS] is really going to have to look at security", she said.
A database created by the Washington Post reports 17 school shootings from January 1, 2018, to March 25, 2018 - the last entry in the database. "He didn't feel safe".
Cuffie admitted to the crime and surrendered at the school, according to authorities.