What if you could strengthen the weakest parents in America? Nine percent more of their children would graduate high school, 6 percent fewer would have a child by age 19 and 3 percent fewer would have a criminal conviction.So conclude Richard V. Reeves and Kimberly Howard of the Brookings Institution in a report called "The Parenting Gap."Parenting matters, they write. It matters to individual children, who are more likely to succeed at all stages of life if they have strong parents. And it matters for the collective health of society.Policies to help weaker parents do a better job can be investments in opportunity and equality, the authors write.It is no surprise that family income predicts parent quality. The wealthiest parents score as the strongest when researchers evaluated more than 30 years of data. They looked at family income and educational level, but also things such as the nature of meal times and whether there are books and toys in the home.The difference in parent strength among income levels was most pronounced at the bottom of the economic scale. Parents in the bottom income level trailed middle-income parents much more than middle-income parents trailed the wealthiest group.The same thing happens in education. The difference is greatest at the lowest levels.Having plenty of money eases everything from buying groceries to hiring a lawyer. There's no mystery there.But parenting among higher-income families is not just about buying things.As family income rises, parents tend to spend more time with their children. And they spend it differently from the lowest-income families, the report says.Higher income parents talk with their school-age children for three hours more a week than low-income parents. Their infants and toddlers spend about 4 1/2 more hours a week in new and stimulating places. Children in wealthier families hear more words per hour from birth, giving them a huge vocabulary to work with when it is time to learn to read. Highly educated mothers tend to tailor activities to the developmental level of a child more than mothers with a high school education.The lesson from this report is the same thing I've learned over a career spent reporting on efforts to help children and families: Help parents, and you help kids.Whatever helps parents shed stress, gain health, earn wages and be the sort of nurturing providers they aspire to be, can make a huge difference in a family, a community, a state.The trick is to discover which things help.Actually, that's the easy part. Tons of things have been tried and evaluated over the years.Home visitor programs are my favorite. That's where a knowledgeable person -- a nurse, social worker or other professional in a relevant field -- literally visits families at home. They help parents solve problems, keep an eye out for developmental delays and share knowledge with parents about child development, discipline, routines, nutrition and learning. I've watched them expand and contract over the years in no relation to their effectiveness.The Brookings report mentions them at length. Some are more demonstrably effective than others, but seven evaluated by the federal government were found to make a difference: Early Head Start-Home Visiting, Family Check-Up, Healthy Families America, Healthy Steps, Home Instruction for Parents of Preschool Youngsters, Nurse Family Partnership and Parents as Teachers.This documented knowledge of what makes a difference over a lifetime should lead state and local policy.The real trick I've long suspected is overcoming a collective resistance to paying human beings to do this sort of work. Can anyone truly help people to be the sort of parents they would like to be, rather than shaming, incarcerating, drugging or ignoring them? Research and experience says yes. How many of us actually believe most struggling parents long to do better? That's the question. Miller, the Gazette's editorial page editor, can be reached at firstname.lastname@example.org.