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?
Students at the design faculty I worked at were are well versed in 3D design, often a 3D printer is something students even invest in.
One of the reasons that they do is the difficulty in planning and reserving a printer at the faculty, especially when at the end of the semester there is a gold rush for having their prototypes printed at the faculty's high-end printer. Another task is to well advise and control the printability of prototypes, and the reasons why they are using the 3d printer.

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?
Some of the 3D models I worked on were very advanced and required a lot of editing before being well printable that took much more time than planned.