Parents have been warned about buying unnecessary add-ons as retailers take advantage of the requirement of many schools for students to have a laptop or tablet.
So-called "Bring Your Own Device" (BYOD) policies have added hundreds of dollars to back-to-school costs for families.
The total back-to-school bill can now top $1,000 per child at some state secondary schools.
Retailers have long targeted parents' stationery budgets by aligning themselves with schools, and the same tactic is now used by those selling electronics.
Some chains encourage parents to buy devices as part of a more expensive "bundle" package.
But Consumer New Zealand has warned that a core selling-point in these deals is not generally needed under existing consumer law.
"I think in most instances those schools are trying to do the best deal they can - for their students and for school funding," Consumer chief executive Sue Chetwin said.
"But at the end of the day that's probably not their area of expertise, and sometimes these deals aren't as good as what they seem."
Noel Leeming partners with 86 schools as a "preferred supplier". One, Rangitoto College, displays its products and deals on the school website.
Families have been invited to a special event at the Noel Leeming Albany store, and the college receives a 2.5 per cent donation on any item purchased.
Noel Leeming maintains a pool of loan devices for Rangitoto customers who are still under warranty. The school's website recommends that those who purchase from Noel Leeming take an extended three-year warranty option "to ensure maximum use of this benefit".
The extended warranties are also part of "bundle deals" which are advertised to parents.
Ms Chetwin said it was Consumer's view that such extended warranties were not generally necessary as they did not deliver protection that was not already provided by the Consumer Guarantees Act.
Noel Leeming spokeswoman Julia Bell said the extended warranties provided benefits "over and above" the act.
"For example, any electrical or mechanical faults that are covered during the manufacturer's warranty period [typically one year] have cover extended up to four years, whereas the Consumer Guarantees Act only covers customers for 'a reasonable period'."
Customers were also covered for malfunction due to normal wear and tear while the act "only requires products to be durable for as long as most people would expect".
Customers were also covered if their product suffered a power surge or sulphur damage. Ms Bell said customers also benefited from 30-day price protection - if they found the same product at a competing retailer for a lower price, they could claim the difference plus 10 per cent, which was not provided for under the act.
Other retailers promote BYOD products through schools. Harvey Norman sells bundle packages that include "product care replace", its extended warranty version. Cyclone Computers has as an "optional extra" an extended warranty and accidental damage insurance.
Rangitoto College principal David Hodge said the school made clear that parents could buy from any supplier, and had moved to a Google Drive format to ensure cheaper devices could be used. The college had talked to Noel Leeming about an expectation that they would offer proper servicing of equipment.
• Orewa College Year 8 to 12 students must bring a laptop or netbook. iPad Air is recommended.
• Mahurangi College Students encouraged to bring any internet-capable device that can be used in learning.
• Rangitoto College Year 9 and 10 students must bring a device (not specified, but no smartphones).
• Auckland Grammar School Senior students who require a computer for a specific course can bring a laptop, otherwise BYOD not allowed.
• Auckland Girls Grammar School Students encouraged to bring a device, however not compulsory.
• Mt Albert Grammar School Year 9 students required to bring a personal computing device. The school's "device of choice" is the iPad.
• Lynfield College Years 9, 10 and 11 required to bring a device with a screen size more than 25cm.
• Waitakere College Year 9 students need an internet-capable device.
• Macleans College Students can bring a device but this is voluntary.
• Pakuranga College All Year 9 students must bring their own device to school.
• Epsom Girls Grammar School Year 9, 10, 11 and 12 students must bring a laptop, netbook or tablet with a full operating system.
• Alfriston College Parents encouraged to provide a device. School provides Chromebooks at ratio of 1:2 within class.
Schooling costs a surprise to immigrants
The Kims found the cost of uniforms, stationery, donations and technology eye-opening. Photo / Brett Phibbs
The cost of New Zealand's free schooling came as a surprise to Joel Kim and his wife Esther Lee, who moved here from China last year.
Mr Kim, who worked in marketing for a business in Guangzhou for about 15 years but is now completing tertiary study, said the fact state schooling is free was stated during the immigration process. However, with two children about to start school, his family will shell out thousands of dollars for costs including uniforms, stationery, donations and technology.
Their eldest, 13-year-old Ellie, will attend Westlake Girls' High School. Uniform will cost at least $500, not including shoes, and there is a donation of $475 for one year.
The family will also buy a laptop or notebook for the school's "Bring Your Own Device" policy - adding a further $400 or $500 to the total.
Daniel, 11, will be at Takapuna Intermediate School. His uniform cost $400 and there is a $600 donation for two years of schooling.
Despite the cost, Mr Kim, whose wife Esther is working as a part-time hairdresser, said his family, originally from Korea, were very happy to have access to New Zealand schooling.
It was a main factor in their desire to move here. Schooling in China and Korea centred on rote learning.