He returned to Cambodia with a teaching certificate .
He taught for a time at the Lycee Sisowath , and went on to become director of studies of the National Teaching Institute , part of the University of Phnom Penh .
Returning to Cambodia with a teaching certificate , he taught for a time at the Lycee Sisowath , and went on to become director of studies of the National Teaching Institute , part of the University of Phnom Penh .