Taj played middle school AAU for Wichita Razorback under Coach Steve Winters.
Gray attended Wichita High School East and as a senior led his team to the Kansas Class 6A state title, earning tournament MVP honors.
He was also named Kansas High School Player of the Year after averaging 20.9 points and 15.5 rebounds and 6.4 blocks per game during his senior season.
Averaging 18.1 points, 10.8 rebounds and 3.3 block per game, he led Redlands to a 35–2 overall record and a national runner-up finish.
Gray was named Big 12 Preseason Player of the Year before the start of his senior season and averaged 14.2 points, 7.7 rebounds and 1.6 blocked shots per games which were all team highs.