Math Medics
S.o.s. Math: Reducing Fractions
Explains step-by-step how to reduce fractions. Gives examples and exercises to practice this skill.
Other
Help With Fractions: Simplifying Fractions
The rules for simplifying fractions are clearly explained at this website. An explanation of how to simplify improper fractions is also included. This is an excellent place to get step by step explanations for working with fractions.
Wyzant
Wyzant: Fraction Simplifying Calculator
This WyzAnt applet allows the user to input fractions--improper or mixed numbers--and have the calculator reduce the fraction or convert it into a mixed number. A good resource for checking students work.