For fathers, it's "the best of times and the worst of times."

So says the National Fatherhood Initiative of Gaithersburg, Md., echoing the opening lines of Charles Dickens' "A Tale of Two Cities."

Today, many dads are more engaged than ever in their children's lives. They put bread on the table, as their grandfathers did, but they also diaper the baby, coach soccer and help with birthday parties.

At the same time, father absence has hit record levels. About 25 million children -- roughly one in three -- are not living with their biological fathers, according to the U.S. Census Bureau.

Until recent decades, fatherhood was one of the most venerated social institutions in America. But today it's under assault. The reasons range from the sexual revolution and economic changes to the rise of the divorce culture. Sixties-era feminism also has played a role, with its view of men as expendable and of traditional sex roles as oppressive. If men and women are the same, who needs dad?

Now a mountain of social science evidence is confirming what our parents and great-grandparents understood: Dad's presence is central to kids' well-being. Children with involved fathers have lower rates of juvenile delinquency, substance abuse and early sexual activity.

They also tend to have higher academic performance, greater self-control, more effective ways of dealing with frustration -- even better wages and greater empathy as adults.

Both boys and girls benefit from their fathers' involvement. Math competence in girls appears to be linked to early connections with the father. Daughters with engaged dads also tend to reach puberty later. Early onset of puberty is associated with higher rates of depression, teen pregnancy and alcohol consumption.

What's so special about dad? Kyle Pruett of Yale University explains in his 2000 book, "Fatherneed."

Pruett points to differences in the ways that fathers and mothers discipline their offspring. Kids need both approaches, he says.

Moms tend to discipline by stressing the "relational and social costs" of bad behavior, writes Pruett. He uses the example of a mother whose young child pushes food on the floor. Her response is likely to be, "Do you ever think about how much work it is for me to clean up the mess when you throw your cereal?"

Dads, on the other hand, tend to focus on the "mechanical or societal consequences" of misbehavior. A typical fatherly response to a whining child is, "Don't ask me for help if you aren't willing to do your share."

Moms and dads also tend to play with kids differently. Mothers' play is more toy-centered and instructional, whereas fathers encourage exploration and novelty-seeking. Dads love to wrestle and roughhouse. They can make even daily chores like dressing, bathing, diapering and bathing "more intensely physical and playful," writes Pruett.

In addition, fathers tend to encourage kids to master tasks on their own, while mothers are more likely to help a fretting child sooner. If a child is searching for the final ring for a tower, writes Pruett, mothers may push it into his or her reach, while fathers often wait, encouraging the child to work through the frustration and complete the task. When teaching kids to ride a bike, he adds, dads are more likely than moms to set a child back on the bike seat after a fall.

I've heard it summed up this way: When mothers see their young ones scrambling up a jungle gym, they tend to call out, "Be careful!" (I know I do.) Dad's challenge is likely to be different: "Can you make it to the top?"

We need more "involved, responsible and committed" fathers. That's the National Fatherhood Initiative's mission. Its "24/7 Dad" program is used by hospitals, churches and even prisons to help dads develop communications, parenting and relationship skills.

How to jump-start father involvement? Dads need to be educated about the vital role they play in their children's lives, says Vince Dicaro, spokesman for the Fatherhood Initiative. "The message is 'Your kids need you,' but many dads haven't heard it."

The struggle to reengage fathers is related to a larger phenomenon -- the loss of our traditional model of virtuous manhood. For 3,000 years, this tradition has taught that a real man is self-controlled, brave and prudent. Such a man defends and protects his loved ones, while also cherishing and respecting them.

A century ago, Theodore Roosevelt captured this vision of manhood while reflecting on his own father's towering influence in his life: "I would have hated and dreaded beyond measure," he wrote, "to have him know that I had been guilty of a lie, or of cruelty, or of bullying, or of uncleanness, or of cowardice."

"Gradually," Roosevelt concluded, "I grew to have the feeling on my own account, and not merely on his."