BOULDER (Colorado) - ON weekday mornings, the Cristol Chemistry Building at the University of Colorado is a hive of activity. Every hour, hundreds of laptop-toting students file in and out of its theatre-style lecture halls, where classes are scheduled back to back.

In all, there are 33 courses at Colorado with 400 students or more. Three have more than 1,200. Most are broken into sections, but even those may have hundreds of students. One chemistry course is so big that the only place on campus where everyone can take the final exam at once is the Coors Event Centre, Colorado's basketball arena.

Such arrangements are here to stay on US campuses.

To get everyone through their coursework, monstrous class sizes are unavoidable.

That does not have to be a bad thing. At their best, giant classes can be effective and inspiring - a way to get the best teachers in front of the most students.

Rare successes
But according to Carl Wieman, who won the 2001 Nobel Prize as a physicist at Colorado, such successes are rare.

Students often tune out and are turned off. Charismatic lecturers get good reviews but, the data show, are no more effective than others at making the most important concepts stick.

Most remarkably, when it comes to teaching not just 'facts' but conveying to students the scientific approach to problem-solving, research shows that students end up thinking less like professionals after completing these classes than when they started.

'In a very real way, you're doing damage with these courses,' Mr Wieman, now a leading voice for reform, said in a recent interview.

Why are so many big classes broken? One reason is faculty and departments closely guard their absolute power over teaching, and there is no central body in the United States or even on campus to direct reform.

Many reforms also take money. If there were enough money, big classes wouldn't exist in the first place.

Accountability
But state and federal policymakers are clamouring for more accountability and better graduation rates, and if faculty don't step up, bureaucrats might. Big classes are the obvious place to focus.

The National Centre for Academic Transformation, or NCAT, estimates that the 25 most common college courses - in subjects like economics, English, psychology and the sciences - account for 35 per cent of four-year college enrolment nationally. That means a lot of people are taking a relative handful of courses.

Colorado, with a long tradition on innovative science teaching, is one of a number of campuses making significant changes in how at least some large introductory courses are taught and organised.

Others include Maryland, MIT, Virginia Tech, Clemson and the University of Alabama.

The reforms go beyond simply reducing class sizes or encouraging lecturers to speak with more animation, though that's an element.

Independent learning
Details vary, but one theme is a shift from a passive model of absorbing a lecturer's words to a more active one where lecturers guide and measure, but students learn the material more independently.

It's not necessarily popular with students, but the cognitive research says it is the way to make learning stick.

'In a traditional course the faculty are doing all the work and the students are watching,' said Carol Twigg, president and CEO of NCAT, which is working with hundreds of universities to improve giant courses.

'In a redesigned course, students are doing the work and faculty are stepping in as needed.'

Mr Wieman is at the vanguard of the reform movement, but it's really his second career. In his first he was a researcher with a rare distinction: He produced a new state of matter. Most people know the three most common states of matter - solid, liquid and gas.

But cooling rubidium nearly to absolute zero, Mr Wieman and Colorado colleague Eric Cornell formulated the first Bose-Einstein condensate, a state in which several thousand atoms align perfectly and behave as a single 'super atom.'

After his Nobel, Mr Wieman could easily have focused on lab work or training a cadre of elite graduate students.

Talking abour teaching
But Mr Wieman uses his clout to secure invitations to talk to his fellow scientists - about teaching. He has become one of several physicists to take up the cause, along with Eric Mazur at Harvard, Edward Redish at Maryland and Robert Beichner at North Carolina State.

Mr Wieman wears tennis shoes and walks everywhere like he's in a hurry. He is.

'I have ridiculous, grandiose visions,' he said, speaking in his temporary office overlooking Colorado's football stadium. 'I want to change how everybody learns science. I won't get into how this will save mankind, but it may.'

The problem, he said, is that scientists stop acting like scientists when it comes to their own teaching.

In their own research, scientists hypothesize, measure - then use data to figure out what works. But for teaching, 'they're immediately willing to make generalisations about the thousands of students who've been through their class based on the two that talked to them last week,' Mr Wieman said.

There's no magic bullet, but measurement is the key.

'We're in this new era of engaging in this as a scholarly enterprise,' said Noah Finkelstein, a young Colorado physics professor who has worked with Wieman to revamp a class he teaches.

'Most faculty haven't been taught education is a scholarly enterprise. Most faculty have been taught education is an art, not a science.'

'Clickers'
One of the tools of the new science is 'clickers,' handheld voting devices now used on at least 700 campuses nationwide, according to manufacturer eInstruction. They let teachers pose mid-lecture multiple choice questions and instantly evaluate if students are grasping the material.

During a recent morning lecture in Colorado's General Chemistry 1131, Professor Robert Parson spoke for a few minutes, then posed a multiple-choice question to the class of about 250.

The question, like others he used, was designed by a team of science-learning experts with trick choices that signal if students are falling for common misconceptions.

The results of the 'vote' popped up on an overhead screen.

Then, before revealing the answer, Prof Parson had students break into small groups to discuss the answer and vote again.

The group did well, and he moved on. If it had performed poorly, he would have reviewed the material.

Perhaps the biggest challenge in college teaching is bridging the gap between an often brilliant expert and students new to the subject. Clickers help remind teachers how a novice sees their material.

'You realise how many people don't know something you forgot you didn't know 20 years ago,' said Barbara Demmig-Adams, one of four Colorado professors who teaches a general biology course with 1,300 students and who introduced clickers this year. -- AP