Inside the school, another teacher receives the numbers and then relays them to a group of students, each with an assigned number. As the children’s numbers are called, teachers hustle them outside to their parents’ cars, identified by number tags dangling from the rearview mirrors.

Saucon Valley Elementary, located in a woodsy community near Bethlehem, Pa., has turned school traffic into a science. Some 125 parents pick up 150 children, some as young as five years old, in just eight minutes each day.

Across the country, school parking lots are getting increasingly congested. For one thing, the population of grade-schoolers has been swelling. And because of concerns about letting children walk the streets untended and the safety of schools in general, more parents are taking to driving their kids.

And more schools are trying to crack the gridlock. New elementary schools now devote up to 40% of their land to parking, up from less than 20% a decade or two ago. Some are designing separate traffic loops for buses and for kindergartners just as airports have separate loops for taxis and buses.

The problem: schools get virtually all their traffic in two short bursts each day. In the middle of the day, a parking lot might look overdesigned, says architect Michael Hall of Fanning/Howey Associates Inc. of Celina, Ohio, which specializes in school design. "But when they’re in that 20-minute peak flow period, it can be a zoo if they’re not designed correctly."

Older schools built for smaller populations are struggling with that very problem. At 13-year-old Blalack Middle School in rapidly growing Carrollton, Texas, traffic became a big problem when the school added 400 sixth-graders a year ago.

This year, traffic flow was further impeded by a major road-paving project right in front of the school. At the same time, Blalack principal Edward Chevallier says he has deliberately limited public access to his school this year because of safety concerns arising from the Columbine High School massacre. Students and parents now use one entrance, forcing most parents to use a single lot. What’s more, fewer parents are letting their children walk or take the bus to school, Mr. Chevallier says.

"Parents have gotten concerned with the school shootings over the past year," he says. "They want to make sure their child is dropped off by someone they know."

All this made for a traffic meltdown on Blalack’s first day of school. School administrators quickly devised a triple-lane system delineated by orange cones that funnels 300 to 400 cars plus several buses through the parking lot twice a day. For awhile, Blalack even had a teacher out in the street directing traffic around construction obstacles--that is, until they warned the school that it would be liable for any accidents resulting from bad directions, Mr. Chevallier says.

Each morning, assistant principal Roylinn Harris stands in the entrance to the parking lot, dodging cars and buses like a matador as she directs them into the proper lanes. "I dance around them pretty good," says Ms. Harris, who keeps up a constant banter with parents as they drive by.

The system seems to be working. Despite the construction, most parents are dropping off their children in five minutes or so this year, faster than in years past.

Other schools are getting so crowded that trafffic jams are inevitable. For example, 23-year-old Niguel Hills Middle School in Laguna Niguel, Calif., was designed for 1,000 students but today has 1,763. The principal and teachers help direct traffic, but parents and school buses still face waits of up to 45 minutes. At the same time, residents of the surrounding neighborhood complain that their streets are plugged up by the congestion.

At a nearby elementary school, an an-gry parent worried about being late to work nearly ran over the school’s principal, who was directing traffic, says Daniel Crawford, assistant superintendent of the Capistrano Unified School District. The school considered filing charges against the parent, but decided not to after he met with police and apologized. "We’re witnessing some road rage," Mr. Crawford says.

Mr. Crawford doesn’t see the traffic problems getting any better until the 43,626-student district—which is growing by some 2,000 students annually—builds more schools in the next couple of years. Even in his new schools, Mr. Crawford says, he can’t devote any more space to drop-off zones without "taking away from classroom space."

Saucon Valley in Pennsylvania is a new school, but it posed particularly daunting traffic problems because it was built on a small parcel of land next to a middle school and a high school. When veteran principal Douglas Koch saw his new school under construction earlier this year, he realized that the drop-off and pick-up area in front was inadequate. Mr. Koch tallied the number of parents picking up children each day, and calculated a line would form for nearly half a mile in front of the school every day—a line that would block school buses from leaving. "It would have been chaos," Mr. Koch says.

So the principal decided to turn the rear playground, accessible to the street by a service road, into a second pick-up area. Kindergartners and first-graders would be picked up in the front, older children in the rear.

In action, it looks more like a factory than a school. First a line of eight to 10 cars pulls up in the playground. Then a teacher brings out a group of students sequenced so the first one in line goes to the first car, the second one to the second car, and so on.

While the buses and cars whisk children away from the front and rear of the school, children walking home leave by two en-trances on the side of the school, keeping them away from the pick-up zones. The re-sult is the entire 870-student school goes from dismissal at 3:10 p.m. to empty at 3:18 p.m.

"It’s like a well-oiled machine," says Roseria Frey, Saucon Valley’s assistant principal.
Parents and relatives of children were skeptical at first, but were quickly won over. "This is really great," says Kathryn Werkheiser, who picks up her nine-year-old grandson from school two days a week. "You won’t have to get out of your car in the wintertime."

Mr. Koch, a trim 57-year-old with the meaty forearms of a former college wrestler, walks around the school each morning and afternoon, making sure parents stop in the right places to pick up their children. He believes traffic flow affects how parents view the entire school.

"No matter what happens within the four walls, if things don’t go smoothly (with the traffic), they think the school is a real mess," he says.