Twenty-eight boys were killed when three bombs hit the town on September 29 1942, along with two teachers and two civilians.
A well-attended service at St Mary’s church included a reading of a personal memoir from the day of the bombing and a song performed by pupils from Petworth Primary School.
The congregation then walked to the cemetery in Horsham Road to hold a minute’s silence and lay wreaths at the mass grave where some of the boys and the then headmaster, Charles Stevenson, are buried.
Guests were invited for a reception following the memorial at the primary school.
Attendees included Canadian high commissioner Lieutenant Colonel Simon Rushen, in recognition of Canadian soldiers’ efforts rescuing boys from the rubble following the bombing.
The Toronto Scottish Regiment and other Candadian units had been posted to Petworth during the Second World War and the tragedy formed a long-standing link between the town and the regiment.
A annual rememberance service is held at the graveside, but the 75th anniversary saw some attend for the first time.
Survivor John Wakeford said it was good to have the event marked with something more substantial.
He said: “I think they’ve done us proud, I think it’s been very very good.”