In 1912 Rees was appointed as one of Her Majesty's inspectors of schools and thereafter spent over forty years in post, responsible initially for Brecon, Monmouth and Newport.
Later, as deputy Chief Inspector for Wales, he was an influential national representative advising many governing bodies at county level on a wide range of technical issues.
[10] At the outbreak of World War II Rees succeeded Sir Robert Webber[11] as M.O.I Director for Wales[12] but in 1943, after ill health obliged him to reduce his workload,[10] he moved to Island House, Laugharne.
From that ancient building, even in later semi-retirement, he continued to conduct selection interviews for ex-servicemen and graduates seeking entry into the teaching profession and also wrote several works on ecclesiastical history.
He was named after his famous great-grandfather Caleb Morris[13] of [1] where he was himself elected honorary Deacon and about which he co-authored a history with his brother Stephen in 1959.