Not only can the comings and goings of the 350 teenagers at the two public charter schools here be watched from a monitor in a small room next to the main building's reception area, but they can also be seen remotely over the Internet. Every night, someone in Jackson, Miss., home of the company that installed the cameras, watches over the buildings half a continent away.

Sometimes the schools' executive director checks the cameras from her home. And if a crime occurs, the computers at the Fresno Police Department can display an immediate picture of what is happening.

As security becomes an ever more pressing concern, schools across the nation are seeking new ways to provide a sense of safety to students, staff members and parents.

''The reality is that today's educators face greater threats to safety than ever before,'' said Ken Trump, a school security consultant in Cleveland. ''Threats range from bullying to school shootings, and now terrorism and war.''

Security equipment can include two-way radios for school staff members and metal detectors and panic buttons with a direct connection to the local police department. A few schools with special concerns about abductions or terrorism are turning to identification cards that can hold bar-coded biometric information like fingerprints.

Mostly, however, schools are making use of increasingly sophisticated video cameras like those at the Fresno campus, home of the W.E.B. DuBois and Carter G. Woodson charter schools. The Web-connected cameras here are among the most advanced available, their images viewable by anyone with a computer, Internet access and the proper password.

Perhaps it is a reflection of how security-conscious the nation has become that remote monitoring of students has so far raised few concerns about privacy.

On the contrary, security experts and administrators who use the cameras say, students and teachers seem to appreciate the increased sense of security. And in some cases, administrators say, having cameras around has modified students' behavior.

The systems are expensive. A network in a single building can cost around $30,000 to install. Fresno's cost was $35,000, plus $350 a month for nighttime monitoring by CameraWatch, a company specializing in security systems for schools. Some school districts are buying much more extensive systems. Biloxi, Miss., for example, has spent $1.2 million to put a security camera in each of its nearly 500 classrooms.

While Biloxi may be an extreme case, ''cameras are probably one of the better investments that most middle and high schools can make,'' said Mary Green, a security specialist at Sandia National Laboratories in Albuquerque who works with schools. She estimated that 30 percent of high schools and 15 percent of middle schools now have video cameras, although most are not as sophisticated as those used in Fresno. (Elementary schools have lagged behind, she added, with less than 2 percent using cameras.)

Security experts and even those educators who use the cameras acknowledge that no system can deter a person or group intent on violence. But that has not dampened interest in the systems. ''I don't know that I've ever visited a school where they didn't immediately say, 'So, tell me about cameras,''' Ms. Green said.

For years, cameras that record video images on tape loops have been a fixture in stores and banks, intended for deterring crimes and as an aid in identifying suspects after a crime occurs. Some schools have been using them for similar purposes.

The Fresno cameras were installed in the hope of deterring graffiti vandals, who began defacing the buildings soon after the schools opened in 2000. Linda Washington, executive director of Agape, the company that runs the two schools, said that after the cameras began operating, petty crimes decreased, but graffiti vandals simply moved to areas not covered by the cameras.

Administrators, teachers and students quickly realized the cameras' value in helping create a greater sense of security. That feeling is generated in large part by the system's real-time remote-monitoring capabilities.

Ms. Green said that feature seems invaluable as the 1999 shootings at Columbine High School in Littleton, Colo., linger in the public memory. Security experts who have analyzed the Columbine shootings, in which two students killed 12 fellow students and a teacher before committing suicide, say that the police response was hampered because it was unclear where the shooters were.

''When you're thinking of the kind of horrible tragedy like what happened at Columbine, you need the real-time,'' Ms. Green said.

Gary Jones, assistant principal of the middle school in Reeds Spring, Mo., said it was the remote, real-time monitoring that he found most attractive when he was investigating camera systems.

''If something happened, I wouldn't have to go into the building to find out what was going on,'' Mr. Jones said. ''We're a little more prepared.''

Reeds Spring installed a system for the school district that monitors four buildings. To pay the $68,000 bill, voters passed a bond measure.

In most schools, cameras are placed sparingly in places known to attract crime or where security may be a concern: hallways, stairwells, common areas and parking lots. Cameras are customarily installed at entrances, too. At the Fresno campus, cameras are affixed to entrances, placed in hallways and positioned inconspicuously in computer labs.

Giving a friendly wave to what she took to be a camera (it was an alarm) above a hallway door, Leah Cherry, 18, a senior at W.E.B. DuBois, said the cameras' presence had changed her behavior and that of her schoolmates.

''You don't ditch your class,'' she said. ''You don't try to smoke in the hallways and you don't bring illegal things to school, because you'll get caught.''

Some schools are installing cameras in greater numbers, like those covering every classroom in the Biloxi school district.

The system, a fully digital version that the district paid for with bonds, state gambling revenue and money from a federal program to bring Internet access to schools, can store up to 20 days' worth of images. The cameras have real-time functions as well.

The Biloxi cameras, 800 or so in all, act as silent witnesses to any number of transgressions, including spitballs, theft, vandalism and bullying.

''Right now I can walk over to my computer and tell you what's going on in any facility in my district,'' said Dr. Larry Drawdy, the Biloxi superintendent of schools. The Biloxi Police Department has the same ability, he said.

Dr. Drawdy said that since the cameras were installed, students have occasionally confessed even before the cameras pointed a finger.

''We have kids coming up and admitting to things we don't even have on camera,'' Dr. Drawdy said.

Privacy concerns have for the most part been minimized. ''Our teachers don't have a problem, the parents love it, and the kids all know it's there,'' Dr. Drawdy said. ''We've had little or no question about it.''

Nor have schools encountered much resistance to another kind of security technology that is beginning to make its way onto the premises: identity cards with two-dimensional bar codes containing information that can include photos, fingerprints, personal information and iris scans.

Preventing kidnappings is one reason schools buy the systems. ''There's a huge issue now of child abductions, and schools are interested in combating that crime any way they can,'' said Chuck Lynch, a vice president at Datastrip, the company that supplies the cards and the portable scanners that go with them. Datastrip has sold the systems to a Jewish day school in New York and two schools in Florida.

''With all the recent events, terrorism and 9/11, and some of these children having parents who are fairly high-profile people, the parents felt this was something they wanted to pursue,'' said the principal at one of the Florida schools, a private middle school in the Orlando area. He requested anonymity to protect the privacy of families with children at the school.

The Orlando school has been using the cards for nearly three months. A total of 300 were issued to students, parents, nannies and anyone else authorized to pick up a child. Each card contains a color photograph and other identifying information. But plans to add fingerprints were delayed. ''It felt too encroaching,'' said the principal. ''We decided, let's get everybody comfortable with it, then reinvestigate that.''

Public schools, on the other hand, generally must be more circumspect about security expenses. ''With the way school budgets are going, they're lucky they have locks on doors,'' said Mr. Trump, the security consultant.

But for Ms. Washington of the Fresno charter schools, the choice was clear. ''We can say we don't have money, but you have to put money into school safety,'' she said, ''You have to find money in your budget.''

However reassuring such systems may be, whether they discourage violent crimes is doubtful, say even those who have come to rely on them.

''The security may be false in some way,'' Dr. Drawdy said. Those who go to school and open fire on teachers and fellow students are looking for attention, not hoping to escape, he said. ''You could put the National Guard out there and it might not deter them.''

Despite the violence in Columbine's recent past, the school's own surveillance system remains limited. Before the shootings, the school had security cameras in the cafeteria for monitoring lunchtime activity. They have been replaced with a $30,000 system of 24 cameras throughout the school. There is no remote-monitoring capability. The cameras are used as a deterrent for small crimes, and for investigations.

Rick Kaufman, the director of communications for the Jefferson County public schools, of which Columbine is one, underscored Dr. Drawdy's point.

''Cameras aren't going to stop the kind of mayhem, chaos and murder that Eric Harris and Dylan Klebold did,'' Mr. Kaufman said, referring to the students who did the shooting.

He acknowledged that real-time remote monitoring might have helped during the incident. ''But who foots the bill?'' he added.

Ultimately, Mr. Kaufman said, no amount of technology can substitute for the human touch in stopping crime and violence in schools. ''The greatest deterrence is students who report it,'' he said.