Chips, pizza, lumpy custard... Everyone has their own memories of school dinners, but since Jamie Oliver's efforts to improve the standard of meals available for children, there has been a sense among legislators and campaign groups that 'something must be done.' This has led to a string of reports and initiatives from various bodies, all of them looking at how improvements can be made to existing school food provision.
The immediate response from the DfES was to set up the School Food Trust; their website is a fantastic source of information with up-to-date news, plus facts for both staff and parents, as well as detailed research reports. The Caroline Walker Trust is another group with an interest in this area (although their remit is broader than just school food).
For a really detailed research report on the subject, try reading School Meals in Primary Schools in England or Turning the Tables: Transforming School Food. Or for a study of how nutrition can be linked to children's educational achievements, take a look at this document from 2006: What is the Relationship between Child Nutrition and School Outcomes?