This model of DNA is more detailed than most paper models designed for students.  Here you can see every atom!  You can see how and why the bases connect, and you can see the difference between ribose and deoxyribose.  Explaining the 5′ and 3′ directions is easy because the carbons are numbered.  The downside of this model is that it is flat, not a 3D helix shape, but I have yet to find a 3D model that can also show all the atoms, so I took the downside here in favor of making the chemistry visible.  You can always twist your model when it is done.  (Ten rungs for each full twist.)

Each rung is a little over 10 inches (25 cm) across. If you need a smaller model, you can tell your printer to print at a percentage less than 100.

NOTE:  This project is included in the “Cells” curriculum, and in “Mapping the Body with Art” module 1.