Days after Danica McKellar had scored exceptionally well on her first calculus midterm at UCLA, a classmate tapped her on the shoulder and said, "'Excuse me, aren't you that girl ...'

"That question always ends with '... from TV?' " says McKellar, who played Winnie Cooper on the long-running ABC series "The Wonder Years."

But this time was different.

"Instead it was, '... who got the high score?' It just blew me away. Something clicked that told me (math) is something that I love, I'm good at it, it's fun, (and) I get to redefine myself."

McKellar co-wrote a theorem and earned a bachelor's degree in math summa cum laude in 1998 before resuming her acting, with a recurring role in "The West Wing." Now 32, she has written a math book for middle school girls, "Math Doesn't Suck" (Hudson Street Press, 2007, $23.95).

With "Teen" -magazine-like cover blurbs such as "Are you a math-o-phobe? Take this quiz!" and "Do you still have a crush on him?", McKellar's book won't be mistaken for the British Journal of Physics, which published her theorem.

A former "Teen Beat" columnist, she uses beading to explain prime numbers, shoe shopping to describe multiples and tangled necklaces to describe complex fractions. Personality quizzes and a math horoscope also factor into her formula.

"I don't feel like I'm talking down to girls at all," she says. "I remember being that age like it was yesterday, perhaps because part of it was documented on television. I feel like I was talking to me at that age."

McKellar wrote all the math problems herself and published math notation in her own, "female" handwriting. "One of the messages I want to give to girls is that math is for them," she says. "My approach is not to say turn your back on glamour and makeup and boyfriends and all the other things girls are thinking about. I'm trying to say, 'Look, I think all that stuff is fun, too. I like shopping, I like makeup, and I like boyfriends, and I like all that girlie stuff. And by the way, why should there be a contradiction between that and being good in math?'"

Looking back, McKellar sees she had lots of advantages: She enjoyed math, attended an all-girls prep school and had supportive parents, including a mother who was good at math. But she still feared math in middle school. Even after she got 5 out of 5 on the Advanced Placement calculus BC test, college math initially intimidated her.

"I should have thought, 'If not for me, who else was the math class for in college?' But I didn't look at it like that. I didn't see myself belonging there. I can't imagine why that would be, except for all the messages and expectations that our society has and gives about women in math. My image of mathematicians was not something I associated with me at all."

McKellar entered UCLA intending to study film, but majoring in math did a lot for her personally. Save for one A-minus in a graduate math course, she got straight A's, including a course in topology (involving geometric properties) taught by Terence Tao, who won math's Fields Medal in 2006. The work she put into her math studies helped her develop an identity apart from entertainment when she really needed it.

"In the acting business, people can take things away from you. Careers can go up and down .... But I knew that math, and the intelligence and education that I got, was something that was just mine, and no one could take that away," she says. "It was really important to me because I understood at that point in my life why it was so difficult for so many child actors to move on, in a balanced way, to adulthood. You've got this skewed vision of how the world views you."

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