A quick printing project like this one can help demonstrate abstract concepts like fractions with clear concrete resources. Check out Fraction learning kit (Bruchrechen Lernmaterial) by tuempl. (And also Fraction learning kit with braille by knape.)
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.