Around one in six secondary school pupils are going without breakfast, a study suggests.
It raises concerns that skipping breakfast will leave youngsters struggling in lessons and more likely to become disruptive.
The findings are contained in a new report by the Local Authority Caterers Association and ParentPay, based on a survey of 10,000 UK parents.
It shows that 15% of secondary school pupils are going to school without breakfast - the equivalent of around four pupils in a class of 30. In primary schools the proportion missing out is 3.9%. Girls are more likely to skip the meal than boys (13% compared with 10.7%), the report adds.
It concludes: "Students going without breakfast cannot be at their best for learning during morning lessons and so can be less attentive and a disruption in class."
The report, commissioned to mark National School Meals Week, also found that parents are taking a keen interest in what their child eats at school, but many are still wary of free school meals (FSM).
Nearly nine out of 10 (89.4%) parents questioned said their overall impression of a school meal was either good, or OK, while 80% wanted more information about what their child had eaten for lunch.
But almost one in six (14.8%) of parents with children eligible for FSM - a measure of poverty - said they did not take up this entitlement. The main reasons given by parents were that they have a family meal in the evening, their child likes to eat with their friends and that they were worried their youngster would be identified as being on FSM.
Judy Hargadon, chief executive of the School Food Trust, said: "One of the most welcome findings here is that so many of these parents are taking such an interest in the food their children eat at school - this has never been more important for keeping standards high.
"With school food no longer inspected by Ofsted, the influence of parents is very powerful for demanding that every child has a good experience at lunchtime. It's vital that they use it - because when children eat better, they do better, and how they feel about lunch can make or break their entire day at school."