With an abacus they can see the calculations and not just wait for technology to tell them.
Educators today use the theory of Multiple Intelligences.
The theory’s eight currently accepted intelligences are:
* Spatial
* Linguistic
* Logical-mathematical
* Kinesthetic
* Musical
* Interpersonal
* Intrapersonal
* Naturalist
See http://en.wikipedia.org/wiki/Theory_of_multiple_intelligences
The way I reckon it an abacus positively exercises five of these eight!
A digital calculator, as used in most math classes today, exercises ZERO of them, and impairs at least one: Intrapersonal.