Schools watchdog Ofsted found standards had "slowly improved" in a minority of schools with primaries raising their game faster than secondary schools, many of which have poor canteen facilities that resemble "fast food" outlets. Some food cooked off-site is "lukewarm" when served.
School meals have become a big political issue after campaigning by TV chef Jamie Oliver. A survey for Ofsted found only 13 per cent of parents thought the quality of food served in English schools was good or better.
But the inspectors also express concern over how parents' attitudes can undermine the healthy eating message pupils learn in class. One year-nine girl feared her father would brand a healthy stir-fry she had cooked at school "rubbish" that should be "given to the dog".
Their report says: "No matter what a school offers through breakfast clubs, snacks and lunches, the significant majority of children's food and nutrient intake comes from home.
"Parents have the foremost responsibility to monitor their children's diet and weight and influence their eating habits and lifestyles.
"Parents also control the amount of money a child has to spend, and have a responsibility to influence the choices their children make."
The inspectors found the best schools limited the availability of unhealthy food like chips, monitored lunch boxes and had consistent healthy eating policies throughout the school day.
Food technology classes were too often dominated by "boring" theory with little time spent learning to cook.
When pupils did get to try cookery, exercises were often limited to baking cakes, buns and pizzas because the ingredients were cheap.
But the inspectors praise Hipperholme and Lightcliffe High School, near Halifax, as offering a good example of how the subject should be taught.
The Education Bill, to be considered by MPs tomorrow, includes measures aimed at improving school meals.