A former director of charter schools overseas is urging New Zealand not to introduce them here.
Robert Wilson directed three charter schools in the US, for a company with more than a dozen there and other public-private partnership schools worldwide.
Mr Wilson said he spent 10 years repairing the damage they caused.
"I had to go into three separate schools to rebuild a structure, where the previous incumbent had no education background in schools."
Mr Wilson, who is Scottish, is a physics teacher at Nelson College. He has been principal of Wainuiomata, Taita and Cashmere high schools.
He was called in to direct charter schools and public-private partnership schools in the US, Iraq, the United Arab Emirates, Pakistan and the Jordanian city of Amman for Sabis - a company that owned a ran charter schools worldwide.
He said it would be "horrendous" for New Zealand to follow suit.
Mr Wilson told the education and science select committee today he opposed charter schools because there is a lack of proof they improve learning outcomes, a lack of quality staff, principals are not educated, a lack of transparent funding and a lack of parental voice.
Mr Wilson opposes unqualified and unregistered teaching staff being allowed to teach in charter or partnership schools, and he opposes any school having a principal without a teaching qualification.
The Education Amendment Bill passed its first reading in Parliament late last year, and is now before the education and science committee.
It would create legal recognition for a third type of school in New Zealand's public education landscape - the charter school, now officially called "partnership schools".
The bill gives special powers to 'sponsors' who would be permitted to have no educational background, but will set the rules and staff pay rates.
The sponsors and the schools would be exempt from public scrutiny and the Official Information Act.
Mr Wilson said he witnessed first-hand the destruction caused by charter schools, and said they did not improve student achievement.
"I had to work with a constant string of graduates with no training and no understanding of how to operate in the classroom. The turnover was horrendous in all of the countries, with the majority of the 'teachers' competing.
"Those who remained lasted perhaps another year before their lack of classroom knowledge either led them to leave or they did not have contracts renewed."
He said trained staff spent long hours working with untrained staff to help them in classroom management, lesson preparation and stress relief.
Staff worked long hours, which resulted in poor performance in the classroom, according to Mr Wilson.
"I cannot understand why children's education is being put at risk by allowing schools to employ untrained people to be put in front of children.
"In many cases, the school had been run on an industrial model, with outputs relating to finance, numbers and test results. This produced a dysfunctional situation."
Wellington Act Party member Stephen Whittington said there was evidence charter schools had worked in New York.
When asked by committee members if he has read the Massey University study into charter schools, he said he had not.
Convenor Professor Emeritus Ivan Snook said analysis in the Massey study used evidence similar to the Government, and found charter schools had potential to cause harm to Maori and Pacifika students.
"It is quite common for charter schools to lead to an increase in inequality based on culture, race or socio-economic status," he said.