Thousands of headteachers are warning of a "school funding crisis" in a letter reportedly sent to millions of families in England.
More than 7,000 heads have warned parents of worsening cash shortages in a joint letter to 3.5 million families, the BBC reported.
In the letter, organised by the WorthLess? campaign group, they are said to claim a request to meet Education Secretary Damian Hinds was rejected due to time pressures.
The Department for Education said school funding in England was "at its highest ever level".
Siobhan Lowe, head of Tolworth girls' school in Surbiton, Surrey, said she has been forced to clean the school, wash the toilets, serve in the canteen, and can no longer afford a deputy headteacher.
She told BBC Radio 4's Today Programme: "I think what people need to understand is, as a headteacher you're almost embarrassed that you can't support the students in your school.
"It's a terribly embarrassing thing to admit that you don't have the money, because you need to provide an education for the students.
"But why am I embarrassed? It's not my embarrassment that I don't have the money, it's due to the fact I'm not given the money to provide for the students in society."
Ofsted chief inspector Amanda Spielman later told the programme: "Schools are working certainly with less money than they had four or five years ago. It's a really tough challenge for them adapting."
She said that "being open and listening to what people are saying is something that is always valuable" when asked if the Education Secretary should meet with headteachers.
A report from the Education Policy Institute (EPI) earlier this year found that almost a third of local authority-maintained secondary schools are in deficit, with one in 10 of them carrying deficits that represent more than 10% of their income.
It comes as Labour MP for Birmingham Yardley, Jess Phillips, tweeted about her son's school having to close early on Fridays.
A Department for Education spokesman said: "School funding in England is at its highest ever level, rising from almost £41 billion in 2017-18 to £43.5 billion by 2019-20.
"In addition, standards are rising; the attainment gap between disadvantaged students and their more affluent peers has narrowed since 2011; the proportion of pupils in good or outstanding schools has increased since 2010; and our primary school children have achieved their highest ever score on international reading tests."