Research different number systems that have been used at different times in history: Egyptian, Babylonian, Greek and Roman, Arabic, Indian, etc. How and when and by whom was decimal notation invented? Learn different conventions for representations of fractions. (The problem of Egyptian fractions.) See [Neugebauer, 1969], chapters 1, 2.
Another interesting source is Number Stories of Long Ago, [Smith, 1919], aimed at elementary school kids. A thorough read of this book, and how it might be used in elementary education might also be a nice subject for a project.