There are calls for sanitary bins to be introduced in primary schools after research found one in 16 Kiwi girls, some as young as eight, get their period while at primary school.
The first-of-its-kind data from the Ministry of Health's 2014/15 NZ Health Survey shows girls are getting their first period at a younger age, lining up with international trends.
Dr Sarah Donovan, from Otago University's public health department, has been studying the data and says there is a serious need for sanitary items to be made available for young girls while they are at school.
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"A lack of access to sanitary items is a serious and hidden equity issue which needs to be addressed," she says.
"It's really a matter of child rights that no girl, of any age, should miss school because her family could not afford menstrual products."
International data already shows the average age of first periods is decreasing, with factors such as increasing body mass index (BMI) in young girls considered a likely contributing factor.
Children in hardship could also be particularly affected, Dr Donovan says.
"We know children in lower socio-economic groups are at a higher risk of obesity through being less able to afford healthy, nutritious food."
KidsCan says demand for sanitary products in primary schools is increasing with many parents on low incomes struggling to afford the items for their children.
The children's charity has also analysed its own data. This year alone, 329 schools across the country were supplied with more than 16,000 boxes of pads, tampons and liners.
More than 30 percent went to primary and intermediate schools.
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Sanitary items were added to the list of 'essentials' provided to schools more than three years ago, after it was found girls were staying home from school because they didn't have any products, KidsCan Chief Executive Julie Chapman says.
"It is an absolute tragedy that girls are missing school because they have their period," Ms Chapman says.
"Education is their ticket out of poverty, and they shouldn't be falling behind because of a lack of access to sanitary items. With the help of our donors we're working hard to change that."
The Government's drug-buying agency, Pharmac, rejected a request to fund women's sanitary items in April last year as it believed the items weren't medicines.
Since then, supermarket chain Countdown has cut the cost of its in-house sanitary items in a bid to tackle period poverty.
Papatoetoe West School teacher Lizzy Lockhart says a girl's first period can often be a frightening time.
"There's still so much stigma around bringing it up and being the one kid in the class who has their period, and feeling like that means something is wrong with you."
Ms Lockhart says it's a huge relief when she can supply girls with free sanitary items.