Almost a quarter of a million children who are registered for free school meals are not eating the dinners, campaigners have warned.
While the number of youngsters registered for free lunches has risen slightly, the proportion who are actually taking up the meals has dropped, according to the Children's Food Trust.
It warned that more must be done to ensure that families who are eligible for the meals are registering, and that their children are eating them.
The Trust said its analysis of official local authority data, published by the Department for Education, reveals that 1,307,455 schoolchildren (17.1%) were registered for free school meals as of January this year. Of these, 82.7% were taking up the dinners.
This means that 225,690 pupils were not eating the free dinners they were registered for.
In January last year, slightly fewer pupils (16.9%) were registered for free school meals, and of these 83.2% were eating the lunches, with 215,000 youngsters missing out.
The Trust's head of evaluation Jo Nicholas said: "Not only is it always a concern to see children living in poverty missing out on a nutritious meal at school - which research shows improves their focus and performance in class - but their school lunch could also be their only proper meal of the day, particularly important when so many families are struggling to make their food budgets stretch.
"We know there are still many reasons why families don't sign up for school meals, and why they don't always opt to take them up once they have registered, but it's so important that schools are getting the help and encouragement they need to do something about this.
"Ultimately, it's about getting the whole school meal experience right for children, so that every child wants to have school meals - whether they pay or get them free."