The total bill of educating a youngster in a state school has soared by more than £6,000 in the last five years, it suggests.
The latest Aviva School Sums index reveals that families are paying out more than £1,600 per child per year for school lunches, out of school care such as breakfast clubs, transport, uniform, shoes, textbooks and sports kit.
This adds up to parents spending £22,596 on sending a child to school between the ages of four and 18, compared with almost £16,000 in 2008.
The most expensive outlay is out of school care, which costs £558 per child per year on average, followed by taking a child to and from school at £379 and school lunches at £369.
School uniform costs families £108 on average each year, while shoes cost a further £78, sports kit £59 and textbooks £63.
In addition to the cost of schooling, parents need to find another £1,268 per year for extras such as sport, music and visits, Aviva calculated.
Louise Colley, protection distribution director for Aviva, said: "The majority of children in the UK are taught through the state system, but it's clear from our research that this is far from 'free' for parents. With even the basics adding up to more than £1,600 per child per year, this is a significant challenge, particularly for parents on lower incomes.
"Every parent wants to do the best for their children, especially when it comes to schooling, so it's no surprise to see that many parents are funding educational extras such as overseas trips and additional tuition. All the same, it's shocking to see how quickly the cost of these adds up."