He was speaking to at least 600 party faithful in Wellington at the first of 14 hustings meetings for the four contenders, and got a rowdy reception as MP for Wellington Central.
Mr Robertson said the party had to not only be about fairness, but aspiration as well.
He wanted New Zealand kids to be the most connected in the world and the most confident, to top the PiSA (Programme for International Student Assessment) results in maths and English and to all have a second language.
Leadership contender Nanaia Mahuta said she knew a lot of people who would write her off in the contest.
She said she did not want her bid defined by her gender, culture, religion or sexual orientation but by Labour values of opportunity and aspiration.
Ms Mahuta said the challenge facing Labour was not just about leadership but how to build a team.
"We are stronger when we work together and are united."
Supporters of each candidate greeted the party faithful with leaflets.
Mr Robertson's leaflet said "new generation to win" and featured a picture of him and his preferred deputy, Jacinda Ardern.
Ms Mahuta's said "stronger together".
Andrew Little's leaflet said: "This is our chance to make change for the good."
David Parker's said: "It's about a fair go for all New Zealanders."
Labour Party president Moira Coatsworth welcomed former MPs to the meeting, including former Prime Minister Sir Geoffrey Palmer.
- By Audrey Young of the New Zealand Herald
