A diorama is a model representing a a scene with three dimensional figures usually inside a shoe box or some kind of box. Initially when asked to create a diorama students have this fantastic vision of their box could look like but then when constructing it with paper, scissors and glue their vision begins to fade and then it often becomes the role of the parents to make the box look better.
Why not give students technology that will enable them to express their creative thoughts? I use Google Sketch Up with my students and it is free! Here is a link to my Google Sketch Up unit of work and below is a video that introduces the free software.
If teachers are insisted on students creating dioramas, then why not integrate film as well? My son who is in was recently asked to write a narrative, make a diorama, show his diorama to the class and then read his narrative. He did as the teacher asked but he also used his iPad to create a short video to share, making his diorama part of his narrative. The video is a draft, but it gives you an example of you to make the experience richer.