[Maths-Education] importance of physical materials for mathematics in elementary school

[Katherine Mackrell]

I have just met a Serbian teacher who informs me that there is pressure to
remove the use of physical materials in design technology in elementary 
schools and to replace
these with computer software.

Much as I love 3D computer software, I share his concern with regard to
students' basic understanding of 3D space and the impact that this change
might make on students' mathematics.  Could people please send me arguments/
references, etc that would summarise the importance of using physical
materials for developing mathematical understanding at the elementary level? 
  It's so obviously important to me that I'm not quite sure where to start!

Thanks

Kate