 He then joined the staff at Southern Illinois from 1988 to 1989 before becoming an assistant coach under Lon Kruger at Kansas State in 1990.McCullum followed Kruger to Florida where he was an assistant from 1991 to 1996, and once more worked under Kruger at Illinois from 1996 to 2000.In 2000, McCullum was named the head coach at Western Michigan where he compiled a 44-45 record in three seasons, including a berth in the 2003 NIT.