The students in Michael Dubson's physics class at the University of Colorado fell silent as a multiple choice question flashed on a screen, sending them scrambling for small white devices on their desks.
Within seconds, a monitor on Dubson's desk told him that 92 percent of the class had correctly answered the question on kinetic energy, a sign that they grasped the concept.
Clickers — not unlike gadgets used on television game shows — first appeared in college classrooms over a decade ago and have since spread to just about every college and university in the country thanks to cheaper and better technology.
But as clickers have become commonplace, a divide has emerged over just how sophisticated they should be.
Some professors like Dubson endorse simple, straightforward devices that stick to multiple choice questions. Others embrace fancier models or newer applications for smart phones and laptops that allow students to query the professor by text or e-mail during the lecture or conduct discussion with classmates — without the cost of purchasing a clicker.
Those preferring simplicity say pared-down remotes reduce distractions in a multitasking world, while others say fighting the march to smart phones and digital tablets is a losing battle.
Clickers first gained popularity in large science lecture halls as a way of gauging whether students understood the material. They have since migrated into smaller classrooms and can be found in nursing and other professional schools. Even middle schools and high schools are using them.
Research at the college level has found that students like using the devices and attendance often goes up. But results are mixed when it comes to learning. Some evidence suggests clicker use has led to only modest gains in retention and test scores, while other studies have detected little or no improvement, according to a November article in the North American Journal of Psychology.
"It's not magic," Dubson said. "It can be used very badly or well."
What works with the clickers, according to Dubson and other professors, are questions that spark discussion and get students to explain concepts to each other. What doesn't is using them sporadically or for rote memorization. Students also become resentful when they're used to play attendance cop and spring pop quizzes.
At the University of Colorado, 20,000 of the 30,000 students on campus own clickers. They can be found in music, environmental studies, communications, comparative politics and law classes.
Dubson sprinkles in clicker questions every five or 10 minutes in his calculus-based introductory physics, a tough required course for physics and engineering majors.
He's using a concept called peer instruction. Instead of lecturing for 50 minutes and taxing attention spans, questions are projected on a screen, students gather in registered "clicker groups" to discuss them, then students use their clickers to respond.
"We want students to get in the habit of translating the messy questions into plain English, to be able to explain it," Dubson said. "Students for the most part aren't used to that."
Clickers get mostly positive reviews in Dubson's class of 250.
"With such an enormous classroom, it's about as close as you can get to a hands-on approach to the material," said Jaris Judd, a sophomore from Blairsville, Ga. "This keeps you more on track and in tune."
William Powell, a junior from Durango, Colo., saw two benefits: "It's good impetus to pay attention and not let your mind wander during the lecture. You can see how other people are doing compared to you ... and analyze why someone may have picked a different answer."
The praise wasn't universal. Even though Dubson keeps the stakes low — clicker questions are bonus points and count for a maximum of two percent of someone's grade — the system by its nature makes attendance part of students' grade, said Maximilian Bondrescu, a Fort Collins, Colo., junior.
"Plus it's an expense," he said. "An extra device to carry around. It runs on batteries and the batteries run out. But mostly I don't like the attendance thing."
Costs range from $35 to $70
CU-Boulder chose the device — which uses the same technology as a garage door opener and has five lettered buttons — because it's simple and durable, Dubson said. One student's stopped working when he spilled Coke on it. He cleaned it with soap and water and it worked fine. Students pay about $35 for them.
More sophisticated clickers run in the $60 to $70 range. Some have gaming features that appeal to the Wii generation and one can record the fastest responders.
Most, if not all, of the handful of major companies in the clicker business are marketing applications that use smart phones or Web browsers to accomplish many of the same functions.
At Central Michigan University, students in an introduction to teaching course use iPhones and iPod touches to answer poll questions and access discussion material on the Web. Students who don't own either device can rent an iPod touch for $30 through the CMU Bookstore.
Several schools — including the University of Notre Dame, Virginia Tech and the University of Florida — have turned to a text-messaging product marketed as a cheaper alternative to clickers.
Derek Bruff, assistant director of Vanderbilt University's Center for Teaching, said simple clickers are great at multiple choice questions. But he's more excited about using smart phones, which allow students to ask questions of instructors, hold back-channel discussions with each other and respond in their own words.
On the other side of the great clicker divide is Timothy Stelzer, an associate professor of physics at the University of Illinois and co-inventor of the iClicker, used at CU-Boulder and 900 other campuses.
He argues that students will be too distracted by other things on their Web browsers and points to a Stanford University study last year that showed undergraduate students are lousy multitaskers.
"You obviously have to make something that sells," Stelzer said. "But it's very possible the excitement and enthusiasm about Web clickers might just kill the whole peer instruction thing."
Harvard physics professor Eric Mazur, a pioneer of peer instruction, said he's sympathetic to both camps. Still, he predicts that clickers will be obsolete in 10 years because nearly everyone will own something like a laptop, tablet or smart phone, and he dismisses the argument that multitasking will be a problem.
"The teacher," he said, "just has to be more interesting than YouTube."