For administrators used to dealing with rickety portable classrooms on trailers, the quality and appearance of modern mobile classrooms may be a pleasant surprise.

Newer mobile classrooms are true modular buildings, not trailers. They don't sit on permanent wheels and axles, so they can be set flush to the ground, instead of requiring steps and ramps to reach the doors and skirting to hide the underside. This alone makes them look much more like a "regular" classroom.

Ground-level access, combined with customized exteriors such as vinyl siding, brick, or stucco, will make your mobile classrooms look like a permanent part of your school, instead of a tacked-on temporary solution.

Here are some other distinguishing features to look for in a high-quality mobile classroom:

• concrete or steel walls
• reasonably-sized, openable windows
• rubber or shingle roof
• modern HVAC systems (not through-wall AC)

Mobile classrooms of old are based on office trailers, the cheapest and most temporary type of pre-manufactured building. They're a familiar sight on construction lots across the country. They range in size from 8' x 20' to 12' x 60' (a "singlewide") and can combined into double, triple, or larger groups.

Office trailers are still used as mobile classrooms, but usually as a temporary solution, not a permanent structure. They have few options for appearance and customization, but they are the cheapest and fastest way to add classroom space.