Kids can learn which fractions are equal, for example 2 1/8 are equal to 1/4 by stacking the 1/8 pieces on top of the 1/4 peace. The more advanced can add 1/4 and 1/8 by putting them onto the plate and counting the sections of the plate.
The most advanced calculation that can be done is something like 1/2+1/6=2/3 by putting the corresponding fractions onto the 3/3 plate.
The default settings worked fine for me on a Makerbot Replicator 2 with PLA and up to 1/10 parts. If you print with ABS you may want to reduce the clearance.
If you want smaller than 1/10 pieces i would advice to download openscad and reduce the size of the text.