McCullar played basketball for Karen Wagner High School in San Antonio, Texas.

In his junior season, McCullar averaged 16.8 points, 6.6 rebounds and 3.8 assists per game, before fracturing his tibia during the playoffs.

[2] A consensus four-star recruit, he committed to playing college basketball for Texas Tech over offers from Houston, Kansas State and Louisville.

[3] McCullar redshirted his first season at Texas Tech to rehabilitate after fracturing his tibia as a junior in high school.

[5] In his sophomore season, he averaged 10.4 points, 6.3 rebounds and 1.7 steals per game, earning All-Big 12 honorable mention.