As a junior attending Modesto Christian High School in California, Hayes was named all-league and all-state. That year he grabbed 31 rebounds in the 2000 Northern California championship game - a California High School record for all divisions. As a senior, Hayes was named "Mr. Basketball" in California and a Parade All-American while leading his team to the state championship game.

Hayes was also named an all-state football player as a sophomore.

Hayes arrived at Kentucky in 2001 after choosing UK over Kansas in a close recruiting battle. Hayes was named to the All-SEC Freshman Team in 2002. During the next three years, he contributed to a resurgence in Kentucky basketball along with Keith Bogans, Gerald Fitch, Erik Daniels, and Kelenna Azubuike. Over Hayes' sophomore, junior and senior seasons, Kentucky accumulated a record of 87-15 (.853), and earned final AP rankings of 1st, 2nd and 7th respectively. During Hayes' senior season, the Kentucky athletics department promoted him as an All-American candidate, using the slogan "All He Does Is Win". Although Hayes was named the 2004 SEC defensive player of the year, he did not earn All-America honors.