Correction: An earlier version of this story misidentified Daniel Tabarez. The story has been corrected.

Caleb Cantres-Maldonado was all of 6 weeks old and just stirring from a nap when his mother propped him up and pointed him in the direction of a picture book.

“Look what I have! See the book?” said Milenka St. Clair, a family support worker who visits Caleb’s Manassas home once a week. “It’s a drum! What else do you see?”

Caleb’s head flopped to one side. St. Clair tapped the page loudly, then moved it left and right and up and down. The baby’s eyes, still cloudy and a little crossed, followed her movements.

“He’s looking at it!” she said. “See? He’s ready to learn!”  

Home visits such as St. Clair’s are preschool in its earliest form. Through programs across the country, nurses, social workers or trained mentors offer support to new or expectant parents and impart skills to help them become better teachers for their children.

While Caleb is not learning to read yet, St. Clair said, he is developing his vision and a lifelong love of books.

The brain develops more in the first few years than at any other time in life, and studies have identified an achievement gap as early as nine months into a child’s life, separating those from rich households and those from poor households, which tend to be more stressful and less stimulating environments. By the time children are 2 or 3 years old, the gap is more pronounced in the size of their vocabularies, their social skills and their emotional abilities, such as to calm down and focus. All are key predictors of later school success.

President Obama’s plan for universal preschool calls for a major investment in home visiting programs, which advocates say can bridge that gap.

Home visiting programs have proliferated in the past few decades, with a few becoming national models. One 2012 study in New York found that children who participated in a home visiting program operated by Chicago-based Healthy Families America were less likely than a control group to repeat first grade and more likely to excel at skills such as following instructions and working well with others.

Other studies have shown a wide rage of social and health benefits, all of which are also related to later school performance, including fewer low-birth-weight babies, less isolation and depression for new moms, and fewer cases of child abuse and neglect. Many programs also help parents pursue additional education or better jobs.

The success of home visiting comes from its highly personal approach, said Deborah Daro, a researcher at the University of Chicago who has studied the programs.

“There is a real value in going into the home and seeing the context that a child is being raised in,” she said. Being there, it’s possible to see whether the baby has a safe place to sleep or whether there are any books in the house, she said.

Caleb’s mother, Antwonette Serguson, was referred to the Healthy Families home visiting program in Northern Virginia by her midwife when she was three months pregnant.

St. Clair started visiting the 21-year-old mother-to-be in her basement apartment in Manassas. She showed her pictures of how the baby develops in utero and encouraged her to eat more fresh fruit and less high-sodium instant noodles.

She brought a baby doll to demonstrate how to swaddle and change a diaper. And she gave her an anthology of stories to read aloud to her fetus. Serguson was surprised at first, but St. Clair assured her the baby could already hear her. So she thought: “Okay, I’ll try it.”

She read a story every day, holding the book above her growing belly.

Often the two women would discuss the stresses and financial strains on Serguson’s young marriage. During a late-April visit, Serguson told her she had gone online to apply for food stamps. She talked about her husband’s pending job application at Costco and the possibility of marriage counseling, which St. Clair said she was looking into.

St. Clair, a Chantilly mother of two college-age children, trained to become a home visitor 13 years ago with Northern Virginia Family Service, which runs the program. She called her job “super, super rewarding.”

After visiting Serguson, St. Clair drove a few miles to her second appointment with Portia Boateng, a single mother from Ghana, and her son, Prince.

With the 7-month-old pulling up on the couch and crawling up the steps toward the kitchen, St. Clair gave Boateng a package of outlet covers and a few safety latches for the cabinets.

She also brought big non-toxic crayons for Prince to play with and a stack of animal pictures. She asked Boateng to print the animal names in English and Twi, her native tongue, and showed her how to put them together to make a book.

By 2010, there were 119 home visiting programs in 46 states and the District of Columbia, costing states at least $500 million that year, according to a survey by the Pew Center on the States.

The early-intervention programs got a jolt of federal funding through the Affordable Care Act, which included $1.5 billion in state grants for such programs. Obama’s proposal for universal preschool would add an additional $15 billion over 10 years. It also would dramatically expand Early Head Start, which currently serves 4 percent of eligible children from birth to age 3, and combines home visiting, health services and day care.

Families in Northern Virginia’s program are evaluated according to multiple potential risk factors, such as: Are they first-time or single parents? Are they recent immigrants? Do they have a history of substance abuse or physical abuse? Was the pregnancy planned?

Exposure to high levels of stress early in life can have a lasting impact on children’s brain development and future health, according to a study released by the Centers for Disease Control and Prevention in 2005.

St. Clair said a big part of her job is looking for ways to ease parents’ stress. “They don’t understand how it’s affecting the baby,” she said.

Brittanny Honsinger, 22, and Daniel Tabarez, 23, were both in recovery from drug habits when they met two years ago. Not long after they started dating, she became pregnant with twins. The news was overwhelming and also motivating: They both wanted to make a good life for their children.

But it was difficult. They started seeing St. Clair soon after they came home from the hospital with two tiny baby girls and few notions of how to handle crying infants. Honsinger said she quickly began to rely on St. Clair’s counsel, whether it was advice on how to soothe them, establish routines or develop their motor skills.

“Everything she told me, I did it,” Honsinger said.

They struggled early on to find a stable place to live, and then to pay rent and utilities with Tabarez’s salary as a mechanic. Their water was shut off twice.

St. Clair nominated them for a debt-relief contest, which they won, unloading thousands of dollars of debt this spring. Now they are making plans to start their own car repair business. Honsinger wants to eventually go back to college.

A year later, days after their first birthday, the twins were crawling around a living room full of jumbo Legos, plastic balls and books when St. Clair came by for her weekly visit.

As St. Clair sat down on the carpet, one of the girls climbed into her lap. The other pulled up on her shoulder and reached for her earring. Honsinger said that her own family is far away and that St. Clair is one of the only people who can tell the twins apart.

“Having someone who comes and visits every week and who’s going to be a mentor . . . that makes a huge difference in my family life,” she said.