CHICAGO - Anyone who has ever proudly carried Junior's papier-mache heart into the science fair - only to run into the cardiologist's kid with the medical school model - has seen what happens when the line between parental involvement and parental takeover gets crossed.

Meddling by mom and dad is not limited to budding scientists. It spans childhood, from the Cub Scouts Pinewood Derby to college essays.

Parents may try to help a struggling child, allow a perfectionist streak to get the best of them or get carried away by their own interest in the topic. But one way or another, dad's or mom's work gets turned in, giving the student an unfair advantage.

In response, several school districts are opting for more in-class assignments, studying the meaning of grades and flat-out reminding parents not to do their child's homework.

"It's so tempting to get overly involved," admits Tom Hernandez, a spokesman for the Plainfield schools and the father of an eighth-grader and a high school sophomore. "Your child is a reflection of yourself … so we're all very invested. But it's a delicate balance."

Vernon Hills parent Barb Rosenstock admits that she once helped her son build a project for a school assignment. In her defense, she says, it was on magnetic electricity.

"It had to light up and be magnetic," Rosenstock said. "Come on. They're in 2nd grade."

Her son wanted to build a hockey game, so Rosenstock helped him affix magnets to the bottoms of figurines and rig a light that illuminated when the puck hit the goal.

They proudly took it to school only to find an even more impressive "parent project" displayed alongside theirs.

"They literally had a walking, talking teddy bear. They had made a circuit chip. A circuit chip! You're talking about second-graders," Rosenstock recalled with a laugh.

To be sure, today's parents aren't the first to be heavy-handed. But teachers say the help seems to be escalating for a host of reasons, not the least of which are the push for parental involvement and the pressure to get into good colleges.

Retired science teacher Bill Gillespie has judged dozens of science fairs, and has seen more than his share of adult entries.

Once, he gave high marks to a student who distilled crude oil into gasoline. "She probably used about $30,000 worth of equipment. … It was only later that we found out her father was a prominent engineer," he said.

It's not just about the big project, either. Teacher Cathy Adamsick said one of her third-graders turned in an assignment last fall that was clearly written in mom's penmanship.

She sent it home with a note asking that it be done independently.

When she noticed a flurry of assignments that were either incomplete, sloppy or missing altogether, Adamsick, of Diamond Lake School in Mundelein, said: "Enough."

In February she sent a letter to parents lamenting that students seemed slow to "develop a sense of responsibility and independence."

Many teachers said they are handling the situation by assigning more projects as classwork, which allows students to ask questions and ensures their work is their own.

Not that parental help is always bad. Younger children especially may need a hand, and can learn from a knowledgeable adult.

When a third-grader turned in a fiber-optic replica of the Buckingham Fountain, teacher Jean LeBlanc knew he hadn't built it alone. But when she probed, the boy rattled off a detailed history of the landmark and its operation.

"It was very clear the kid and his father had a great time with the project," said LeBlanc, now principal of Rockland School in Libertyville. "Did the father go overboard? Yes. Did it negatively impact his child's education? Absolutely not."

Steve Griesbach, superintendent of Gower School District in Burr Ridge, said homework and grading practices have become so problematic that he is studying the topic. "You don't know whose work you're grading," he said.

He attributes parental intrusiveness to an increasingly competitive world, pointing out that Northwestern University receives more than double the applications it did two decades ago and admits only a quarter of them compared with 41 percent in 1987.

But experts caution that over-reaching may undercut a student's self-confidence.

"At some point, you have to let go. The longer you rewrite, revise, build and glue for your child, the less likely they'll be able to do it on their own," Griesbach said.

Besides, teachers and students say, parent-cheaters aren't fooling anyone.

When students see a too-slick science display, "We'll just look at each other and say 'Oh, yeah … that's totally a parent project,' said Colleen Maloney, an eighth-grader and science fair participant at Visitation School in Elmhurst.

Julie Marchese, too, has established ground rules for her four sons.

The Vernon Hills mother will buy supplies for science experiments, but she will not build them. She will type assignments - "it would take them hours," but she won't write them.

"It's about instilling the work ethic and an expectation," she said.