Headteacher of Watford Grammar School for Boys, Martin Post, leaves on Friday after 20 years at the school.
Under his management the school has had successive outstanding Ofsted inspections and has consistently appeared in the Financial Times Top 100 Schools.
Mr Post, a former student and headboy at the school during the 70s, said he has enjoyed every single day.
He said: "It's been an absolute joy to come into a school with fantastic teachers, committed students - it hasn't seemed like work at all.
"The school always was outstanding, but it was good to have that recognised in the inspections.
"It has been great to be involved in the major site developments here, such as The Clarendon Muse, the award-winning home of our music department.
"I am always proud of the success of our students. I think our achievements are the achievements of lots of people working together."
Mr Post will be taking up a position as one of eight Regional Schools Commissioners (RSCs) by the Department for Education with responsibility for overseeing the growth of academies in North West London and South Central region and will monitor their performance.
He said the constantly changing educational environment has presented the biggest challenge of his years in teaching, but added this had always presented opportunities.
He said: "Every job has it's struggles, you learn to deal with them.
"We have also had to be increasingly inventive with our finances over time.
"If you do your job properly, the best years of the school are in front of it."
About the educational landscape of Watford, Mr Post said the town's schools are the envy of the country.
He said: "It is hard to find another part of the country with such tremendous schools.
"They are supportive of each other, they have great school leaders - it's really impressive."