Free state education - considered a pillar of French society - costs families an average of pound;100 per child at the start of the year.
School equipment and stationery account for most expenditure, followed by books, according to the report by the Institute of Research on the Economics of Education at the University of Burgundy.
Commissioned by the left-leaning parents' association, the Federation des Conseils de Parents d'Eleves, the report presents the first findings of a continuing national study monitoring educational expenses of 81 offspring aged between two and 22, between July 1998 and June 2000.
The institute has analysed information on 610 families with 1,264 children attending nursery, primary, lower and upper-secondary school. This period, with a peak in September when the school year starts, is when the average expenditure is highest, says Sophie Genelot of the institute.
Apart from 12 children whose parents listed no costs for the return to school, average total spending for pupils was 1,140 francs (pound;102) each, with the maximum for some pupils at college of 9,540 francs (pound;846).
Costs rose as children got olde, with an average of 374 francs (pound;33) at nursery; 665 francs (pound;60) in primary; 1,225 (pound;110) at college; and 1,882 francs (pound;169) at lycee, the only level where pupils supply their own textbooks.
At every stage, equipment and stationery, usually specified by teachers, cost the most - in a few cases up to 6,000 francs (pound;537). Other categories included insurance, sports and other special clothes, class funds and administrative charges.
The study notes sharp disparities in the amounts different families must pay and, it observes, the poorest are hit hardest.
Pupils from the least privileged families are those who are most likely to attend vocational lycees, which often require the greatest financial contribution from pupils.
The report also finds that "certain families, beyond their financial capacities, invest significantly more than others".
Mothers in low-income jobs spend more equipping their children for school than executives or independent professional women, it says.
Georges Dupon-Lahitte, chairman of the FCPE, said the research "confirms that lack of respect for free education is a source of inequality between families. The school generates extreme levels of expenditure; completely unregulated, it has become a market-place."