Although some children will be quick to point out which foods are healthy ones to their parents, not all children have reacted so positively to the recent changes in school lunches. At least, they haven't in the UK. The BBC conducted a survey of secondary schools (middle and high schools) and found that at 60% of them, there had been a drop in the number of students that were opting to buy the school-provided lunch since the switch to a healthier menu. Only 10% of schools had an increase in the number of students taking lunch since the change.
It's too bad that there isn't any US data on this phenomenon after so many schools and school districts have placed restrictions on what types of food are appropriate for kids to have access to during the day, but it seems likely that the problem would be a similar one, especially with older kids who can easily leave campus or go out after school to get the fries and pizzas that they have always had access to at school until now.
The problem is one that will gradually go away over time, as the kids who were used to the "old way" of doing things graduate and the number of students who think that they are entitled to something greasy and unhealthy will decrease compared to he number of children who might actually look forward to a healthier lunch.