"We are pushing very, very hard back home in the States to increase access to high-quality early learning opportunities," he said.
"And I think, frankly, New Zealand is way ahead of us in creating those kinds of opportunities at scale."
The National Government wants 98 per cent of children starting school in 2016 to have participated in quality early childhood education.
More controversially, it has also established the first charter or "partnership" schools. Five of the publicly funded, privately run schools opened this year, with more on the way.
The Herald revealed this month that a US-based firm had expressed interest in setting up a school here.
The US has more than 5600 public charter schools in 42 out of 50 states, and one in 20 students nationally attends one, according to Moody's Investors Service.
Despite being widespread they do face opposition. Newly elected New York City Mayor Bill de Blasio, a Democrat, has been highly critical of charter schools.
Asked for his overall verdict on them, Mr Duncan said there was "huge variation".
"I've visited some amazing, amazing schools that are absolutely closing achievement gaps. We need to learn from those examples and replicate them. [But] when you have low-performing charter schools you need to challenge that status quo as well."
Mr Duncan said the idea for the schools came from union leader Albert Shanker, who hoped to establish "laboratories of innovation". Successes could then be spread to the wider education system.
"I think there's a great opportunity there for this country."
When New Zealand slipped down in the latest Programme for International Student Assessment (Pisa) rankings in December, it provoked alarm and finger-pointing in education circles.
The US rankings have brought similar concern. Mr Duncan said there was no simple answer to improve the Pisa results.
"The Pisa results are a big deal, but for me the real question is what are young people doing beyond high school. Are they truly prepared for higher education, for college? Are they truly prepared for work?"
Personalise lessons for kids, says expert
Teachers must personalise lessons to children with different backgrounds and learning preferences to reverse New Zealand's slide down international rankings, one of the world's most influential education experts says.
Andreas Schleicher has been dubbed the "world's schoolmaster" by international media in reference to the influence of international tests he helped to design.
The deputy director of education at the Organisation for Economic Co-operation and Development, he said a key reason for New Zealand's fall in the Programme for International Student Assessment (Pisa) rankings was social inequality.
One solution was to help teachers embrace the diversity within their classrooms, he said.
"It's the capacity and willingness of teachers to see that students learn differently, and maybe differently at different stages of their development ... It's not about teaching one lesson to a whole class."
Mr Schleicher said some countries, including in East Asia and Europe, had shown it was possible for schools to help students to overcome wider inequality in society.
He said there was "no question" on the statistical robustness of the Pisa results.
