Buy Young, Sell Young

His buddies were intrigued by Microsoft after the antitrust ruling, so he went online to snap up stock. The price jumped $20 a share. It was a classic case of right place, right time. Except that Jason Marchione is not your classic investor. His lucky tip came in the middle of fifth-grade computer class. "There's that famous quote," says Jason, 11. "Buy low. Sell high. Make mad dough."

Once upon a time, the eyes glued to financial news would have had to wear bifocals. But the stock market, like sex, is no longer just adult fare. The Internet pumps quotes, research and trading capability right into Jason's bedroom in Riverdale, N.Y. Nearly half of all households nationwide own stock, up 85% since 1983, and dinner-table drone about performance falls on little ears as well as big. With such incentives, grade-schoolers leap naturally from this-little-piggie-went-to-market to this-little-kiddie-plays-the-market. "This has become a national pastime," says Yale Hirsch, a stock-market historian and publisher of Stock Trader's Almanac. "What's the difference between this and baseball?"

A lot, as it turns out. This pastime carries consequences. Although most children follow the stock market with imaginary portfolios, which are safer than real ones, they can still develop an obsessive need to win. Child psychologist Ava Siegler, author of What Should I Tell the Kids?, says a child's passion for investing must be tempered by parents who convey perspective and values. "If you permit your children to do this," she says, "you have to keep an eye on the downside."

By law, grade school-age kids cannot make legally binding transactions, such as buying stocks. But these new mini-masters of the universe have their ways of playing the market. Jason's mom, for example, opened a $3,500 account but allows him to manage it with her as financial adviser. The average age of Stein Roe Young Investor Fund's 231,248 shareholders is 10. "I check the newspaper to see how the stocks are doing that I invested heavily into," says Bethany Murphy, 11, who came by a hypothetical $50,000 portfolio when her Mount Laurel, N.J., newspaper ran a contest to track readers' stock picks. Bethany lost the contest but discovered a knack for choosing stocks by virtually "earning" a 14% return. Typical of market-savvy children, she has an astute eye for the world around her. She won a national essay contest, advising Stein Roe's portfolio managers to buy Home Depot. A store with a jam-packed parking lot, she reasoned, was likely to have a bright financial future.

Each year nationwide, 250,000 fourth-, fifth- and sixth-graders play "the Stock Market Game," a simulation sponsored by the Securities Industry Foundation for Economic Education. Students open a $100,000 imaginary portfolio to save or "invest" in common stocks. Lisa Ballek, who teaches the game to all fifth-graders at Midland Elementary School in Rye, N.Y., says the simulation brings fractions and decimals to life, especially for students who struggle with math. "They're so excited that they can finally understand what all these numbers mean. That's my favorite part," she says. Her students finished the year with an original musical, Stock Rocks.