He has been a member of the Otago Secondary School Sports Association and gave particular support to two Dunedin schools involved with the Sport in Education Project. He also found time to chair the Otago Secondary Schools Principals' Association.
He led the Dunedin Secondary Schools Partnership, following five years on the management committee and was also chairman of the Alternative Education programme for the Aoraki schools region (1997-2000).
Mr Rennie was a driving force behind the establishment of a Highlander rugby competition for Otago/Southland secondary schools.
Following a cancer operation he chaired the Survivors Committee in helping to organise Relay for Life events for the Cancer Society in Dunedin between 2012 and 2014.
Mr Rennie's education career spanned 46 years and in an interview with the Otago Daily Times last year said his decision to retire came after he said in 2013 he was looking at retirement when he stood, unsuccessfully, for the Otago Regional Council in the local body elections. As an old boy of Otago Boys' High he said returning as rector was a "strong desire" of his and he said he was "very privileged" to have held it.