The mention of “portable” classrooms—or any similar term—puts fear into the hearts of parents with school-age children. Regardless of whether you call them portable, modular, or temporary classrooms, they conjure up unwelcome images of shoebox-like structures with few windows, stuffy air, and noisy and ineffective mechanical systems. But now several design firms, nonprofit organizations, and prefab building companies are developing improved portable classrooms that address these problems and allow schools to expand quickly and sustainably.