Watered down by fuzzy math, "whole language" reading and feel-good grading, public school instruction isn't what it used to be. Therein lies a great profitmaking opportunity: Supply the education that schools don't. Kumon, a Japanese firm that has been selling afterschool tutoring in its home country for half a century, broke into the U.S. market in 1983 and finds no shortage of customers here. Kumon now has 1,300 centers and 194,000 students in the U.S., double its enrollment in 2001. That puts it well ahead of its two main competitors, SylvanLearning and Huntington Learning Center. Most Kumon students are between...