Back at Thornhill high school in the early 1970s, Mike Cowie and his brother Mark didn't pay much attention to their school work. For one thing, the identical twins were working at a garage after school to pay for their cars. They were bored in the classroom and didn't see any practical point in the curriculum. Why, for example, should they memorize a bunch of "common musical terms" from an eccentric music teacher who claimed he let his dog sit in the driver's seat on the way to school? They emerged from high school with C-pluses and a few Bs, just enough to get into university. Their father gave each of them $600 for tuition on one condition -- they get out of town.

Now, their old teachers may be surprised to learn that the Cowie brothers are among Canada's most successful commercial real-estate brokers, doing mega-million-dollar real-estate deals for corporate Canada. From their modest offices in downtown Toronto, they can see some of the high-rise buildings they've helped clients buy, sell, lease or build. You've got to be able to read people, says Mark. "I look for little signs" -- how they sit, how they hold their arms, what they do with their hands, which way they look. Just recently he saw a potential deal start to crater when a developer failed to look a prospective client in the eye as they were shaking hands. "I can understand inflections, how people say things," says Mark. "You can tell if they're hesitating."

The Cowies' success is the story your high school teacher may not want you to know. It's the triumph of the C+ student, the guy who won't be voted Most Likely to Succeed. He's bored in class, and comes home with withering report cards that say things like, "If only he tried harder." His eyes glaze over as his high school English teacher tries to whip up enthusiasm for Shakespeare. He gets lousy marks because he does not want to deliver what the teacher demands. But then, in university or maybe later, he turns on -- and becomes so successful that the school brings him back to give speeches to the kids. High school marks, it turns out, do not predict how well you'll do later in life.

High school marks don't even predict how well you will do in first-year university, says James Parker, who holds the Canada Research Chair in emotion and health at Trent University. "In our culture, high school marks are the most important thing," he says. "Yet if you look at success in first year, high school marks don't predict that very well." A decade ago, Parker started tracking students who arrived at Trent in first year and found that high school marks don't even predict who's going to drop out. "Lots of other things beside high school performance predict achievement later on."

So there's hope for the C+ student in high school. "The truth is that many indifferent students do extremely well in business because the set of skills required to be a good student does not match the set of skills to be a success in the world," says Michael Thompson, a University of Chicago-trained psychologist and co-author of the bestseller, Raising Cain: Protecting the Emotional Life of Boys. He likes to quote the old line: "School is a place where former A students teach mostly B students to work for C students." It may be an overgeneralization, but it has "more truth than educators are comfortable with," he says.

As a psychologist, Michael Thompson spends a lot of time talking to anxious parents in Canada and the U.S. about their children's performance in high school. He keeps telling them that a C+ does not mean the kid is headed for a dismal future. High school grades, after all, measure one thing -- whether the teacher thinks the student has mastered the curriculum. But some kids, especially boys, are just not interested in delivering what the teacher wants. Boys, he says, often think school is "stupid, boring and inefficient," says Thompson. "They're just waiting for it to be over." Girls, on the other hand, do better in school, even though they're bored too, because they want to impress the teacher. Boys, he says, are more active, impulsive and impatient. "They support each others' dislike for school."

So the report card goes home with the C+ marks and the parents fume. Why won't their son do his homework? Is he a loser? Maybe not.

There are innumerable examples of poor students who changed the world -- or made a pile of money. Winston Churchill was famously at the bottom of his class at Harrow, the exclusive English private school. Richard Branson left high school to run a newspaper he founded. Senator John McCain graduated 894th out of 899 in his class at the U.S. Naval Academy. President George W. Bush was a solid C student in his first year at Yale but showed early promise as a politician because he could remember the names of each of the 54 pledges in his fraternity.