Sometimes it takes years of exacting, exhaustive research to prove what common sense might tell us if we only asked.

Here I refer to the results of the largest survey of its kind ever conducted in the United States, released a week ago. It found that students who attend smaller schools tend to feel more connected to their teachers and to one another and are less likely to engage in risky behavior such as drug use, violence or early sexual activity.

The researchers carefully surveyed nearly 72,000 students in 127 representative schools across the country to confirm what anyone familiar with teen-agers knows all along: They need our attention, no matter what they say.

“In smaller schools, students, teachers and school administrators all have more personal relationships with each other,” Robert Blum, director of the University of Minnesota’s Center for Adolescent Health and Development, said in the introduction to the study he authored.

“They know who you are. This is important to keeping kids engaged and a part of school.”

Blum’s research adds to what educators already know about the academic value of smaller school environments that test scores, attendance rates and graduation rates improve when high schools are home to several hundred, rather than several thousand, students. This is especially true for poor and minority students. Smaller schools are a well-tested academic equalizer.

Yet the average enrollment in the nation’s public schools is creeping upward. For elementary schools, it has held steady for the last few years, but at the highest rate in 15 years. For regular secondary schools, average enrollment is as high as it’s ever been in that time frame.

Imagine: There are high schools in this country with more than 5,000 students. That’s the size of a small army. And while schools of that size are rare, the proportion of schools with 1,000 or more students is increasing steadily.

As with everything else in education, there are caveats. Small is better but it is not perfect. Size does not always predict student achievement. And educators themselves don’t agree on the definition of “small.”

But this much is certain: The pressure on schools to grow and consolidate is unabating whether to realize economies of scale in distressed school districts or to absorb burgeoning populations in sprawl communities. Even Congress acknowledged that fact when it recently offered competitive grants to encourage school districts to create “small learning communities” in mega-high schools.

Going even further, the Bill and Melinda Gates Foundation announced last month a $40 million program to create 70 small high schools in which students could also earn college credit. The foundation already had committed more than $300 million to create new small schools and transform high schools into more manageable, personalized communities. Think they’re on to something?

Holly Perry has known about the benefits of smaller schools 18 years, since she became principal of A.M.Y. Northwest, a Philadelphia middle school with about 250 students and a solid academic reputation. Yes, there is a downside to her more intimate environment which is why she was answering the office phone one afternoon this week, when there was no replacement for an absent secretary.

Still, Perry is convinced that size matters and is cost-effective in the long run. As an example, she has tracked how many of her graduates complete ninth grade in one year an excellent predictor of whether they’d eventually receive a diploma. The districtwide average is about 50 percent. For A.M.Y. Northwest grads, it’s between 85 percent and 90 percent.

That achievement might be overlooked by those focused on short-term academic and financial goals. Perry worries that “someone will come in and not understand how schools work that connectedness is essential to community, and community is essential to learning.”

It’s an equation borne out by research and reinforced by common sense. Which, in the musty realm of politics and education, may be just enough to doom it.