These days, you can't be too careful – or can you?

WANTED: Parents to volunteer in their children's schools. Help teachers with reading, after-school programs, and field trips. All volunteers must first pass a security check conducted by the Criminal Records Bureau.

* * *

This ad is mythical, but the situation it describes is real for parents at some schools in England and Wales. According to a new policy from the Department for Education and Skills, teachers and anyone having contact with children in schools must submit to a background check.

No longer can caring parents, most of them mothers, simply show up in a classroom to lend a helping hand. It will be at least Christmas, in fact, before many of them receive clearance to volunteer, because the beleaguered agency handling the security checks has such a backlog of applications.

A large headline in The Independent sums up the frustration many volunteers feel. It reads: "They ask parents to help, then treat us like criminals." Sonia Purnell, a mother who wrote the article under the headline, warns that the required vetting could offend some parents enough to keep them from even signing up. She and others point out that volunteers are always supervised by a teacher and are not left alone with students.

Because a school caretaker and his girlfriend are suspects in the recent murders of two girls in Cambridgeshire, parents are understandably concerned about children's safety. Background checks do offer a measure of reassurance. But is it going too far to demand that parents be included?

An official of Britain's National Association of Head Teachers calls the security checks "a sign of the times." He adds, "This is the price we pay for the need to be ultra-cautious."

But when does ultra-caution cross the line into paranoia? And when does a "better-safe-than-sorry" approach risk causing more problems than it solves? The answers are often not clear-cut.

The mantra for the 21st century has become: You can't be too careful. But wait. Maybe you can. If fear clouds every activity, sowing seeds of doubt and distrust, suspicion can become a way of life.

Suspicion produced a sad ending for three medical students in Florida last month. When a woman in a Georgia restaurant overheard them talking, she thought they might be terrorists and called 911. Police blocked off a 21-mile stretch of Interstate 75, apprehended the young men, and questioned them for 17 hours before letting them go. Although they were found not guilty, the men, who are Muslims, have lost their chance for training at a south Florida hospital.

Another sign of ultra-cautious times: A week ago, as I was taking a flight to Boston, my plane departed late because a clean-cut, neatly dressed passenger in his 30s showed an expired driver's license. He had to return to the main terminal and resolve the issue before the gate agent would let him board.

Those of us waiting patiently on the plane could only wonder: If the photo on the license matches his face, and the name matches the name on the ticket, should it matter if his license had recently expired?

In an age still coming to terms with new concerns about safety and protection, ultra-cautious may be the order of the day for now.

But it will be a welcome moment when a sensible middle ground returns, so that a generous-hearted parent with an hour or two to spare, willing to help a busy teacher at school, doesn't need a security clearance to read a story to a classroom of children.