TITLE: Mathematics seminar for "non-mathematicians"
QUESTION [9 upvotes]: Next term I am leading a seminar for students, who will become teachers for elementary school i.e. for kids of age 6-10. The students in the seminar will have no mathematical background beyond the "Abitur". They are supposed to give a 45 minutes talk on a (not too difficult) mathematical topic, and they have to write an exposition of a few pages. My first ideas cover geometry of triangles, basics around Fibonacci sequences ect. Did somebody on MO teach a similar class already?
In brief: I would appreciate further suggestions for suitable topics very much!

REPLY [3 votes]: Have a look at the exhibition on knots on http://www.popmath.org.uk . I have used this and other material for talks advertised as "How mathematics gets into knots" for ages 8-80: I was then criticised for suggesting one should stop at 80! 
The material I used in a recent general lecture in Kansas (see my my preprint page)  on the Dirac string trick, and the related belt trick  and Phillipine wine trick, and on the pentoil, can be done for any age; it is essential to involve the audience in doing the tricks, or demos. One can also do addition of knots, and analogies between knots and numbers, getting over the point that while knots and numbers are quite different, the relations between knots can be analogous to the relations between numbers.  Note also that my apparatus for the Dirac String Trick was home made: two piece of board, coloured ribbon, bulldog clips to attach the ribbon (in case it gets too tangled). My pentoil was made in a science workshop from copper tubing. 
In giving such a presentation  to children and teachers once, a teacher came up to me afterwards and said:"That is the first time in my mathematical career that anyone has used the word "analogy" in relation to mathematics!"  Thus a real concern is that there is so little discussion about mathematics, and its context.