The average monthly voluntary donation parents are making to school funds rose by £2.45 over the past year from £8.90 to £11.35, a survey suggests.
The charity Parentkind found parents being asked to pay to attend events such as concerts and sports days.
The findings come after Chancellor Philip Hammond caused offence by offering £400m for "little extras".
The government says more money is going into schools than ever before, rising to a record £43.5bn by 2020.
The one-off payment for schools in England would be worth, on average,…