Al Turgeon knows turf.
The Penn State University professor of turf grass management is world-renown, but students don't have to travel to University Park to learn from him.
Some of his classes are as handy as the nearest computer, whether it's in Pennsylvania or China, at home or in a war zone in Iraq.
Since Dr. Turgeon began offering Penn State's first online course in 1998, the Penn State World Campus has grown from the initial 15 students to more than 5,000 enrollments from all 50 states and more than 40 countries.
Penn State's not the only one with a burgeoning enrollment in online classes. Over the past decade, online education has been growing throughout higher education.
Nationwide in the fall of 2005, nearly 3.2 million students at degree-granting institutions were taking at least one course with at least 80 percent of its content delivered online, according to the most recent available survey by the Sloan Consortium, which helps schools improve online education.
That's nearly double the number doing so just three years earlier.
Two-thirds of the schools surveyed had at least some online programs.
Typically, these classes were fully online without any face-to-face meetings. Many are "asynchronous," meaning no one needs to be in the same place at the same time.
In addition, many schools are designing "hybrid" courses that meet face-to-face less frequently than traditional classes but include additional time online.
Gene Maeroff, author of "A Classroom of One" and senior fellow at the Hechinger Institute on Education and the Media at Columbia University, said the hybrids are becoming important because they enhance the "ability to overcome obstacles of time and place."
He said, "I think that higher education is rapidly moving toward the point where there will hardly be a course that doesn't, in one way or another, make use of technology."
That doesn't mean face-to-face classes will be a thing of the past or even that online learning will predominate.
"Classroom-based learning will always have a place, especially for people of traditional age," said Mr. Maeroff. "That's the largest group for whom it's most suitable, and a lot of students grow by being on a campus."
Nor does it mean that distance education is necessarily better -- or worse -- than the classroom.
"It's neutral," said Thomas Russell, author of "The No Significant Difference Phenomenon" in which he examined 355 studies and articles on distance education, dating to correspondence courses in the 1920s. Since the book was published in 1999, he has looked at 50 or 60 additional studies.
While individual students may do better in one or the other, Mr. Russell, also director emeritus of instructional telecommunications at North Carolina State University, said, "There are some studies that show it's superior and a few that show it's worse. But the vast number of studies shows there's no difference."
Online courses appeal to a wide variety of students: adults who have difficulty fitting fixed class schedules with work and family responsibilities; students who aren't near courses or programs they want; traditional college students who are looking for flexibility or want to take advantage of new technology.
With a family in Penn Township and a full-time job on the grounds of the Westmoreland Country Club, John Churchfield, 44, was still able to earn a Penn State certificate in turf grass management in 2002 by taking courses online.
"It's very well-organized, well presented," said Mr. Churchfield, assistant superintendent at the club. "If you put forth the effort, you're going to gain the knowledge just as well as sitting in the classroom taking notes."
Greg Niendorf, 28, of Monroeville, a member of the grounds crew at Oakmont Country Club, earned his turf grass management certificate online in 2005.
"I thought it was wonderful," he said. "I was still able to work on the golf course and take what I learned from class and apply it to the field."
He said he was in touch with his professors "pretty much every day" and enjoyed it more than some face-to-face business courses he took at a community college in Michigan.
But he noted a frequent caveat about online learning: "You definitely have to be self-disciplined," he said.
The types of courses that can be taught fully online aren't necessarily limitless.
In some cases, at least some of the work must be hands-on, such as that for nursing students learning to deal with patients.
But an example of how some barriers have fallen is the violin performance instruction open to a select group of students at the Manhattan School of Music. They take monthly private lessons with virtuoso violinist Pinchas Zukerman, who teaches in person or from wherever he is performing in the world.
The school uses video-conferencing via Internet2, a high-speed network used by more than 200 universities.
The extra-wide bandwidth that permits the fast speeds helps to make high-quality video possible, enabling Florida State University dance instructors to coach dance students at Wayne State University in Detroit and Massachusetts Institute of Technology to collaborate on an advanced engineering degree with the National University of Singapore.
One of the strengths of some online programs is they give access to students who never would have had it otherwise.
"This has made a very significant difference to people who are in rural, remote, underserved places who can get an education where they really couldn't before," said Janet Poley, president and CEO of the American Distance Education Consortium, made up of state and land-grant institutions and based at the University of Nebraska-Lincoln.
Paige Rien of New York City travels too much as a designer for HGTV's Curb Appeal to attend a bricks-and-mortar school.
But Ms. Rien, who has a bachelor's from Brown University, can work on a bachelor's degree in interior design at The Art Institute of Pittsburgh-Online Division as long as she has an Internet connection in her hotel room.
The fact that Duquesne University offers its master's of science in community leadership online makes graduate work possible for Lisa Beam, 34, of Somerset, who is a wife and mother of two small children, works full-time in community services, is a part-time cheerleading instructor and a volunteer.
"I personally love it," Mrs. Beam said. "I would probably not be pursuing my master's degree right now if I didn't have this option."
Ruth Newberry, director of educational technology at Duquesne University, said she found when she taught adult students face-to-face at night school that "they were tired" and there often was no connection with them between classes.
"I saw richer discussion and expressions and articulation and thinking in my online literature courses than I ever got in the classroom discussion," she said.
Some programs wouldn't be offered at all if they weren't online. Duquesne University wouldn't have enough local students for its bachelor's in humane leadership, offered in cooperation with the Humane Society of the United States. But through the Internet, it has 56 active students.
Online courses are most popular at big universities and two-year schools, according to the Sloan survey.
About half of all online students were studying at two-year associate's institutions. At Community College of Allegheny County, the number of students taking online courses has grown from 1,782 in 2001-02 to 7,676 last year.
Leann Zotis, 50, of Kennedy, is working toward an associate's degree in CCAC's dietetic technician program and so far has taken about a dozen online courses. Occasionally, a course includes a few face-to-face meetings, such as a food class that had five Saturday cooking labs.
"It fits with the schedule of a working person who has a husband," said Ms. Zotis, who earned a bachelor's degree in psychology the traditional way at the University of Pittsburgh in 1977.
One of the largest providers of online education is the University of Phoenix, which began as a bricks-and-mortar school in 1976, added online courses in 1989 and has grown to more than 300,000 students -- about half of them online -- and 198 locations .
Todd Cunningham, director of the Pittsburgh campuses of the University of Phoenix, said online education has become more accepted over the years.
He said that as more schools of all kinds add online courses "you start to read more and more articles from highly touted individuals in the education world who have changed a lot of their positions on online education and academic rigor."
University of Phoenix initially focused on business programs and added career-oriented offerings such as health care and criminal justice. It now is preparing to launch into more liberal arts and offer a doctor of philosophy.
Small, private four-year colleges often do not offer many, if any, online courses, because their stock in trade is the close-knit campus experience.
While it has technology resources for its students on campus, Washington & Jefferson College, with 1,517 full-time undergraduates, offers no online courses.
"It's just not the kind of thing we're interested in doing. We feel the students learn more from the direct contact with each other and the faculty," said Jan Czechowski, vice president of academic affairs. "I think the personal contact, the interaction, the communication takes place best when it can be done live and in person."
On the other hand, Chatham University, with an enrollment around 1,900, is moving into online education in a big way in its School of Continuing and Professional Studies.
About a fifth of the university's enrollment comes from online undergraduate and graduate programs in nursing, occupational therapy, health science and professional writing.
"Chatham is land-locked, so it's one way for us to expand our offerings without having to expand physically," said Laura Armesto, vice president for academic affairs.
Some schools offering online programs try to keep such classes small. Carlow University, which offers eight online courses, caps enrollment at 15 "so we can ensure there is the interaction and collaboration among the students," said Denise King, assistant director of instructional technology.
Some schools in the online education business have long histories of offering correspondence courses that relied on the postal system.
The College of General Studies at the University of Pittsburgh began offering correspondence courses in 1972. In fall 2006, it launched PittOnline with 10 online courses and 10 hybrid ones. This fall, 454 students are enrolled in more than 30 Web and hybrid courses.
"We certainly see growth in this area because of our population being the nontraditional student," said Kelly Otter, associate dean of the college.
If you don't need any credits and want to experience online courses for the joy of learning, a dozen courses in various stages of development are available free through the foundation-funded Open Learning Initiative at Carnegie Mellon University at www.cmu.edu/oli.
The open-learning courses provide computerized practice, some simulations and feedback although not from a live professor or other students.
Some other schools, including Massachusetts Institute of Technology and the University of California at Berkeley, have some course materials and lectures available free online. MIT's OpenCourseWare can be found on www.mit.edu. Berkeley's is on www.youtube.com.
Taking at least one online course may become more and more important. "There's talk about encouraging, if not requiring, even our resident students to take at least one online course when they're here," said Dr. Turgeon of Penn State.
"It's a different kind of learning environment. Chances are after they graduate and get into professional work, they'll need to come back and take online courses they'll need for their profession."
Education writer Eleanor Chute can be reached at email@example.com or 412-263-1955.