Comfortable solution, but requires mostly a building dedicated to it.
It can be built by an amateur team (respecting safety rules) or  by a company.

Note that this is not necessarily the solution for reaching a public school. 
In many cases, the institution prefer calling to a mobile planetarium instead of renting a bus to go to a small fixed planetarium...

the planetarium fixed dome of Marseille (diameter: 6m)

Composite hard dome:

http://www.eze-composites.com/realisations-diverses.htm

Metal dome:

http://www.gambato.it