Thomas attended Scotch Plains-Fanwood High School in Scotch Plains, New Jersey during his freshman and sophomore years. For his junior and senior years, he attended St. Benedict's Preparatory School. He led the school to two Prep A Division New Jersey State titles with a 56–3 record in his final two seasons while averaging 14.5 points and 6.5 rebounds per game his senior year. In 2005, Thomas played at the USA Basketball Youth Development Festival where he helped the Blue Team win the silver medal with a 3–1 record. Following his senior year, he played in the 2006 McDonald's All-American game.