When students in Leslie Chernila's English class at the Art Institute of Washington write an essay about the work of Garrison Keillor, she has them send it off to a critic halfway across the country before turning it in. The paper soon returns, complete with comments about structure and word choice.

The service, offered by District-based Smarthinking Inc., is part of a growing educational trend that has millions of students logging on to get assistance with reading, writing and arithmetic. Once a dot-com pipe dream, online education is now maturing into a viable market. More than 2.6 million students in the United States were expected to study online through courses and tutoring last fall, up from 1.9 million in 2003, according to the Sloan Consortium, an online research group.

Burck Smith, chief executive and co-founder of Smarthinking, credits the rise in demand for online educational services to several factors, including an increase in the number of non-traditional students who don't have a lot of time to look for on-campus resources, a more competitive educational landscape in which colleges and schools are trying harder to attract students with additional services and students' greater familiarity with the Internet.

More than 500 institutions, including Anne Arundel Community College, Gallaudet University and the Art Institute of Washington, subscribe to Smarthinking. And the company says it has signed up 19 institutions for this fall, including District-based Southeastern University.

Schools pay Smarthinking for a block of time and offer students free access to the service from a personal computer or a college lab. Colleges signing up for the first time can buy a plan that permits up to 15 hours of tutoring for each student and then adjust its next contract according to usage, Smith said. The company did not disclose the cost per hour.

Terry H. Coye, director of tutorial and instructional programs at Gallaudet University, said his school turned to Smarthinking to supplement its limited tutoring services for graduate students. With many of Gallaudet's deaf and hard-of-hearing students accustomed to learning online, the service was a good fit, Coye said.

Founded in 1999, Smarthinking employs more than 450 part-time instructors from around the world to offer round-the-clock tutoring. Washington students struggling in the middle of the night with a math question may get an answer from a tutor in India, where the morning's work is already underway.

The company says 80 percent of its online tutors have graduate degrees in their discipline. While tutors come from around the world, 98 percent of the writing instructors are based in the United States.

Though some critics might worry that a student could get too much help from someone outside the classroom, the company said it trains its tutors -- who get an average of 15 hours of training -- to guide students through problems and not give away the answers.

The company is not yet profitable, Smith said, but he estimated that sales grew by "35 to 40 percent" last year. The new fall contracts are expected to bring in an additional $500,000 to $750,000, Smith said.

As more students become accustomed to the technology, the competition for online tutoring services is likely to heat up. Already, educational services giants Kaplan Inc., owned by the Washington Post Co., and Princeton Review Inc. have made inroads in the online education market. And Baltimore-based Educate Inc. said it plans to expand its online tutoring service.

"Long-term, there is no reason to believe [online tutoring] is not going to grow as students go online and take classes," said J. Mark Jackson, director of K-12 research at Eduventures Inc., a market-research firm. Because it is a supplemental service rather than a core offering, he said, it is unclear how large the market might grow.

Online tutors are available 24 hours a day for one-on-one help in math, writing, science and other topics. Students and tutors discuss assignments through online chat sessions, using a virtual whiteboard that allows for use of charts, graphs and diagrams. Those wanting help with a paper can submit a draft for feedback, which usually comes back within 24 hours.

Chernila, coordinator for the academic achievement center at the Art Institute of Washington, said she relies on Smarthinking tutors to help students refine their writing. She encourages her students to use the tutors for "another voice and an another opinion." The additional feedback, she said, made for better student work. The Art Institute pays for the service, provided free to students.

Brent Mellecker, 19, a media arts and animation major who took Chernila's literature class, said he was pleased with the responses he received from Smarthinking. But, he said, it could sometimes take up to three days to get a paper back.

"I always asked for the first available tutor online to make sure I got [the paper] back in time," Mellecker said. A few other students also experienced small delays with their essays, Chernila said. But she said it rarely interfered with her class.

Amy Yang, 20, a game art and design major, said she found the comments helpful on her writing assignments and usually received a response from a tutor in a day or two.

Chuck Kleiner, vice president of sales and marketing at Smarthinking, said company records show that 80 percent of the papers submitted from the Art Institute of Washington since 2003 were returned within 24 hours. Kleiner said that records indicated only 4 percent of the papers were returned after 30 hours and that those delays were usually caused when essays were submitted before a holiday break.

Speaking of time, Kleiner said more than 70 percent of questions arise between 6 p.m. and 9 a.m. on weekdays, and on weekends.

"We're available when they can't get help anywhere else," he said.

Tamika Thomas works in the tutoring lab at the Art Institute of Washington. The school uses Smarthinking's service.