Dallas school officials projected six years ago that a billion-dollar bond program would rid the district of many of its 1,913 portable classrooms. Instead, the number has grown. A database lists 2,029 portable classrooms in the district as of November 2007--despite a drop in student enrollment and the opening of 19 new schools under a 2002 bond construction program. More than 30,000 students attend classes in portable buildings. Reasons for the increase include smaller class sizes that require more space and principals who want to keep vacant portables to accommodate spikes in student enrollment.