Slumber party When Boston's Museum of Science invites hundreds of Girl Scouts to spend the night, it's a time for listening, learning, giggling, questioning. And after the young guests roll up their sleeping bags, their hosts hope they'll take home the message that science is fun, and girls can do it.

EVERY Friday and Saturday evening between January and May, they come: little girls shouldering garbage bags with their sleeping bags and assorted dolls and teddy bears inside. After the adult museumgoers leave at 9 p.m. on Friday and 5 p.m. on Saturday, hundreds of Girl Scouts -- ranging from 1st to 8th graders -- have Boston's Museum of Science to themselves. The museum becomes their playhouse, their slumber party, their midnight movie theater, and their classroom for creative lessons on science and math.

Program director Michael Smith says the idea of science museum camp-ins began 15 years ago, when the Center of Science and Industry in Columbus, Ohio, started it (though the children don't actually sleep in the COSI museum).

Boston's Museum of Science designed its program, now in its second year, in an attempt to interest girls in math and science courses -- before they start avoiding them. Co-ed programs, Mr. Smith says, tend to leave girls out in the cold, with the boys tending to say things like, ``You're a dumb girl,'' or, ``Let me show you how to wire that circuit.''

``The stereotypes we've come to expect are real,'' Smith adds. The program tries to emphasize that science ``is a way of looking at the world.'' Its organizers hope the girls come away from their weekend with the message that science is something that little girls can do, too.

On a visit last weekend, it was impossible to tell if the message got through: Ask the Brownies how they like the program and they tend to say things like, ``It was great.'' Ask them what they're learning: some give clear answers; others do not.

Nevertheless, it's obvious enough that these children -- Brownies in the 1st through 3rd grades -- are engaged, amused, and certainly audible, as they sing middle-of-the-night choruses of ``If you're happy and you know it, clap your hands,'' and frequently take up the written offer to push a button to hear the dinosaur.

In the early evening, a few regular museumgoers are still drifting through, mostly parents solemnly escorting their children to various points of interest. But the favored 300 have the air of owning the place. Clad in lavender, pink, and turquoise warmup suits, they skip about holding hands, or run from one end of the building to the other, emitting high batlike shrieks.

A giant tire hangs from the ceiling; the kids experiment to see how many Brownies can squeeze in. Nine of them giggle and squirm while a troop leader takes a picture; then out they dart across the floor; then back into the tire again.

This kind of mayhem inhabits the spaces between more serious, but highly involving workshops, such as Amy Barber's ``Mathmagic,'' where a troop of second graders describe math as ``division,'' ``fractions,'' ``all kinds of problems,'' and ``yuck.''

Miss Barber tells them that the word mathematics means ``to learn science,'' and that math is called the queen of the sciences because all the others depend on it.

Taking out a penny, she begins flipping it, explaining to the girls that the penny has a 1 out of 2 probability ratio of coming out heads. ``The more we flip it, the more regular it's going to get,'' she says. The Brownies eagerly try flipping some pennies themselves. After 130 tosses (13 Brownies flipping 10 times), the ratio is 67 to 63 in favor of heads. ``That's pretty close,'' Miss Barber notes.

In another workshop, David Wood's ``Share Your World,'' a local troop become scientists for an hour. ``When you're a scientist, there's an an easy part, and a hard part,'' says Mr. Wood. ``The easy part is that you don't have to know the answers.''

``But what about science tests?'' several voices shriek.

Mr. Wood explains that what a scientist has to do is to investigate.

``Science is what you do every day,'' proclaims Michael Smith, who runs the Mind Games workshop. ``Scientists are not those people in the movies who have castles. Scientists are you and me.''

To make his point, he engages the girls in what he calls paradoxes of perception, performing such ``tricks'' as making a Brownie disappear in a booth (they do it with mirrors).

On Friday nights, because of longer museum hours, there are 10 workshops offered to 300 girls; on Satur days, 600 girls have a choice of 20 workshops.

Round about midnight, Brownies make up their campsites next to giant DNA models and signs saying ``You are extraordinary,'' under bronzes of animals, and beside a a life-sized model of Tyrannosaurus Rex, as they await the strange experience of awakening in a museum.

In the early morning, tiny nightgowned figures scuttle about in the half darkness, then a fluorescent dawn; soon the museum itself starts coming to life. The probability machine begins dropping balls into slots, demonstrating the principle of the normal curve. A movie giving the viewpoints about wolves of several Minnesota residents in plaid shirts begins talking to itself.

When they leave, what do these girls take away with them? Have they changed their ideas about science?

``I'm much less interested in content,'' Michael Smith says of the program. ``It's a critical age, when they're being told certain things about themselves. If they're told [that science is fun] by role models they can trust, they'll believe it.''