A company that serves meals to 2½ million schoolchildren daily in more than 500 districts nationwide, with multimillion-dollar contracts in both Washington and Chicago, has a history of marginal quality and food-safety scares amid concerns over the nutritional content of its school menus, according to school and company records. Chartwells-Thompson School Dining Services, a subsidiary of the Charlotte, N.C.-based Compass Group, owner of Burger King, Taco Bell and Pizza Hut, is one of North America's largest school cafeteria operators — its contracts with the Chicago Public Schools from 2001 to 2009 totaling more than $289 million and a D.C. operation...