About 2 percent of the students said they'd used an e-cigarette in the previous month, according to a survey done last year. That was up from 1 percent in 2011.
More kids still smoke traditional cigarettes than the new electronic ones, and it's not clear how dangerous e-cigarettes are. It's also not clear from the report how many are using them on a daily or weekly basis.
But health officials are worried. The new study suggests many kids are now getting a first taste of nicotine through e-cigarettes and then moving on to regular tobacco products, they say.
Electronic cigarettes are battery-powered devices that provide users with aerosol puffs that typically contain nicotine, and sometimes flavorings like fruit, mint or chocolate. They've often been described as a less dangerous alternative to regular cigarettes.
Unlike conventional smokes, the federal government does not yet regulate e-cigarettes, although more than 20 states have banned store sales to minors. The devices began to appear in the United States in late 2006, but marketing has exploded in the last couple of years.
The new study — released Thursday by the Centers for Disease Control and Prevention — is based on a questionnaire filled out by nearly 19,000 students in grades 6 through 12 in 2011 and another 25,000 in 2012.
In 2011, about 3 percent said they'd tried an e-cigarette at least once. That rose to 7 percent last year and translates to nearly 1.8 million students.
In contrast, 6 percent of adults have tried e-cigarettes, according to a different CDC survey done in 2011.
Children still are more likely to light up regular cigarettes, though teen smoking rates have dropped in the past decade. More teens now smoke marijuana than tobacco, surveys have found.
But health officials worry e-cigarettes could re-ignite teen cigarette use. They point to a finding in the study that 20 percent of middle school e-cigarette users had never tried conventional cigarettes. When the same question was asked of high school students, only 7 percent had never tried regular smokes.
That suggests many kids experiment with the electronic devices and move on to cigarettes by high school, said CDC Director Dr. Tom Frieden.
"In effect, this is condemning many kids to struggling with a lifelong addiction to nicotine," he said.
Kurt Ribisl, a University of North Carolina tobacco policy expert, was a bit more restrained, saying the results "don't prove that e-cigarettes are a gateway to smoking cigarettes". Another study would be needed to more clearly establish the link, he added.
He said the results may fuel the Food and Drug Administration's plans to eventually regulate e-cigarettes.
Some makers of e-cigarettes said Thursday that they supported regulations that keep the devices out of kids' hands. But some are wary of steps that might affect adult buyers.
Future regulations shouldn't "stifle what may be the most significant harm reduction opportunity that has ever been made available to smokers," Murray Kessler, chief executive of Lorillard Inc., the nation's third-biggest tobacco company and owner of Blu Ecigs, said in a statement.