School meals are small, carbohydrate-heavy and cost more, according to a survey of teachers.
A snap poll of 503 members of the Association of Teachers and Lecturers (ATL) indicates that two-thirds of schools are charging as much as £100 more a year for meals.
The majority (three-quarters) said that school lunches, which are subject to stringent nutritional guidelines, were healthy - but a fifth disagreed.
The results of the poll were revealed at the ATL's annual conference in Manchester, where the take-up and importance of free school meals were debated by teachers, according to the BBC.
The number of children eligible for free school meals is rising as a result of the economic downturn and rising poverty, the poll suggests, and ATL general secretary Mary Bousted said that it was even more important that school meals were of good quality and size.
She said: "But teachers are raising issues about the quantity of the food that children get, about the choice and the quality. Some teachers are saying that children don't get enough food."
"I think it's absolutely the case that children are going hungry and we all know what hunger does to young people's ability to learn."
Dr Bousted called for more inspection of catering services to ensure that meals were of a good standard and size.
Commenting on the quality of school food, one primary school teacher said there were times that meals were good but others when they were "most unappetising", adding: "There are occasions when the portion size is very small and there have been times when portions have run out."
A secondary teacher said: "There seems to be a lot of carbohydrates on offer each day. There are usually chips, pasta and rice available, while vegetables and salad don't seem to be on offer."
On cost, 60% said the price of meals charged to students in their school or college represented good value for money, but about a third (34%) said it did not.
Another reception teacher said that while younger children paid the same price as the older ones, they got much less food and did not get the same amount of choice.
This view was shared by another early years worker, who said: "The young children often get very small portions and very limited choice. Children who come with packed lunches eat a lot more at lunchtime."
Around one in 10 respondents said pupils on free school meals did not actually eat school food, with 44% saying their children did not like them and 41% saying their children preferred to bring their own.
By Janie Manzoori-Stamford
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