The entire process rarely takes more than a few days. Once assembled, the connecting walls and roofs are sealed, utilities connected, and the interiors finished off. Normally most of the interior work was done at the factory, with bathrooms, sinks, interior walls, carpeting, electrical outlets, and such more or less complete on delivery to your site. This can be a tremendous advantage if you are building next to or close to existing classrooms. Where traditional construction can take months, it is conceivably possible to schedule the final assembly of your modular structure over a weekend or holiday.
Future additions are equally simple and convenient.
If your master plan design provides for eventual expansion to four classrooms, but you only need two at the beginning, you will be able to add the last two modules on at any time with minimal disruption. One final advantage to keep in mind is that while modular buildings are not all that easy nor inexpensive to move, they can be taken apart, moved, and set up in a new location. There is even a market for used modular buildings. So build them, use them until you're ready for more expensive permanent construction, then sell them to a worthwhile school that is just getting going. Modular buildings are most often made of wood framing built up on a steel trailer bed.