Marra, who first joined Labour as a teenager, also spoke about his upbringing in Dundee in a family of ardent trade unionists.
He said he made his first leaflet run ahead of the 1987 general election at the age of eight, supporting Ernie Ross MP in Dundee West.
Marra said his grandmother Margaret, one of seven children, slept in a single room and was the only member of her family lucky enough to go to college while the others worked six days a week at the city’s jute mills.
He said he was “forever grateful” for their sacrifice as the opportunity “changed her life” and her education changed Marra’s, two generations later.
He said “not enough lives” in Scotland were being changed by education, and pledged to put Scottish education back among the world’s best.
“It’s no longer the SNP’s priority, if it ever was,” he said.
“I will make Scottish education the best in the world again. Not just steady, not just average, the best in the world again.”