Others have written much more eloquently than I about the difference between the two: http://www.intlnat.com/2010/11/is-it-a-kaleidoscope-or-a-mandala-its-both.html
First, take a look at this video about how to draw a mandala:
How to Draw a Mandala from Premaspace. To me, it is the spiritual intent that is the difference between the two.
I consider my work to be both since I often go into a zen like space in my head when I am creating and choosing kaleidoscopes for this blog. It even extends to the time when I am taking photographs with the intention of creating images for the kaleidoscopes.
I am continually drawn to water and the amazing sycamores which grow here in the riparian zone. Luckily, in the Verde Valley we have a large number of rivers and creeks, including Oak Creek, Spring Creek, Beaver Creek, and the Verde River. The kaleidoscopes below were created from photos of the trees from a recent trip to Page Springs Fish Hatchery with the beautiful grays and brown of early winter vegetation.