1) If you are a teacher in a school working with 3D printing, what are the main difficulties for your students in using this tool?
Having the ability to generate their own structures. I've found it is easy to find a model or part someone else has made but getting students to turn their own ideas into something that is printable has been quite the task. We are using currently using a Dremel Idea Builder to print sculptures made using Sculptris. We have a Skanect with Structure Scanner that we use in conjunction with an iPad and iMac to process 3D scans which has generated a lot of student interest. It seems to me that students are more willing to scan something and then print it or scan something, modify it using Sculptris and then print it than generate something on their own.

2) if you are a teacher in a school working with 3D printing, what are the main difficulties for you to conduct your teaching program or classes?
Getting the students update with the technology in general. There seems to be a fair amount of file conversion or project progression while preparing for printing and the students seem to get lost if it is more than a two step process. We may scan and process something in Skanect, modify it in Sculptris and then run it through Meshmixer to optimize geometry or for support structures before we load it into Dremel's software for printing. I think it the ability to keep track of the workflow is troublesome for them. There is quite a different feel associated with a physical object versus a folder of electronic files.

2) If you are a director or administrative staff, what are the main difficulties for your institution in incorporating this technology for your teaching programs? Are they related with the high cost and number of machines necessary? Is it a matter about lack of skilled staff?
Cost is always an issue. I cannot speak on the number of machines because our experience so far has shown the more time intensive task is in generating an object or project. We have had our printer for about two years and it is used by a dedicated group of individuals. It has been presented more as an option for expression rather than a necessity of a particular class. The staff have become skilled in it use though the software options can be dizzying.