Across the country in San Ynez Middle School in Santa Barbara, Calif., Joe Donahue uses Khan Academy to teach his 7th- and 8th-grade math classes. Donahue requires his students, all on netbooks, to master—at their own pace—25 topics by the end of the trimester. During class time Donahue walks around the room, answering questions and helping those falling behind, as students work on Khan Academy.

He says the difference is huge: "They keep telling me how much they enjoyed what we did. I had kids asking, 'Can we work in here at lunch? I want to finish a concept.' They never did that before."

Despite the different types of education Reilly and Donahue provide, their students are now all watching the same videos and learning the same topics, thanks to Khan Academy. Some education experts say the online classroom is a way to improve math learning in America, where student test scores rank 25th in the world, well behind economic competitors such as China, South Korea, Germany, and Canada. Critics, though, acknowledge Khan's usefulness but don't think it gives American students the innovative, competitive edge they need.

A not-for-profit organization, Khan Academy began when Sal Khan, a hedge fund analyst (see sidebar below), started making videos to tutor his cousins. The videos, which feature Khan's narration explaining a problem as he digitally writes it on a black screen, started garnering a large following. Viewers left comments expressing how much the videos have helped them: "First time I smiled doing a derivative," read one.

Khan started getting letters from parents who thanked him for teaching their children math concepts they had tried so hard to convey, and Khan realized that he was on to something. Homeschooler Reilly likes the simplicity of Khan's videos: "He talks well. He makes it very fun. He draws a little sketch so it's more like he's a human instead of just a math guy."

In 2009, Khan quit his job and started working on Khan Academy full-time. With grants from the Bill and Melinda Gates Foundation and Google, he was able to expand his site, making over 2,400 videos that have been watched more than 63 million times. His next project is to translate all his videos into the world's major languages to provide his classes to anyone with an internet connection.

Last year, Khan added a practice component to the program. The computer continually generates problems until the student correctly answers 10 in a row. Then the student can move on to the next topic or "module." The modules start from addition and subtraction and continue all the way up to calculus. To encourage students to learn more, students can earn badges if they watch a certain number of videos, work quickly, or master a lot of modules.

Teachers have found their own ways to incentivize doing math. When Donahue's students complete a module, he rewards students with stamps by their names and gives them raffle tickets for a weekly drawing for silly prizes. The stamps let the students see where they are in relation to the rest of the class and create competition among the students to do more math. Other teachers give students printouts of the Khan Academy badge to stick on their notebooks when they receive digital badges.

Harsh Patel, a Teach for America member, teaches 5th-grade math at PFC Omar E. Torres charter school on Chicago's South Side. Having watched Khan's videos in high school and college, Patel remembered the site when he started teaching last year. Almost all of his students come from low-income families. The school did not have enough computers for every student, so he scraped together computers from friends and family until he had enough for half his class.

Starting last December, he split his class in half. One half would listen to him teach about math topics for state standardized tests, while the other half worked on Khan Academy. After half an hour, the two would switch.

As the students worked on Khan Academy, they would often ask each other for help on different sections. Patel noticed that students didn't know how to teach their classmates and would just end up telling them the answers. So he handpicked several students who were further along and taught them how to teach others.

Khan Academy also allows teachers to gauge how their students are doing: A dashboard shows how much time students spend on videos and questions, which questions they get wrong, and where they need more help. The dashboard helps teachers like Patel pinpoint where students struggle and pair them with peers who understand the material.

If Patel sees that several students are getting the same types of problems wrong, he meets with them in a small group outside of class time and explains the concept to them. That way, the students who understand the material don't have to listen to things they already know.

Patel found from standardized tests that his students gained one to three years of math knowledge after using Khan Academy for a semester. One student, Jocelyn, had hated math, but quickly caught on to Khan Academy, eagerly mastering modules and continuing on to new topics. She would ask Patel questions about what she was learning: By the end of the year, her scores showed that she advanced 5 ½ years in math.

"This is the way a lot of education is heading," Patel said: "When students are older, they don't need to be spoon-fed what they do and don't need to learn. I think it's moving in a better direction where they choose what is interesting, and they can start learning a lot more independently."

Khan Academy has some critics. Dan Meyer, a former math teacher at San Lorenzo Valley High School, thinks Khan Academy is ideally suited for teaching standardized tests, but doesn't show the bigger picture of how math applies to the real world. He says Khan's lectures and multiple choice questions teach students how to get the right answers, but do not spark a deeper interest in math.

"Math should be developed in an environment where you can dig in, mess around, and play with the numbers," Meyer said. When he taught 9th-grade remedial algebra, each class would focus on solving a problem: One day he put up a picture of a giant pyramid of pennies a man had created over many years, and students were curious as to how many pennies were in the pile. He then taught arithmetic sequences and other topics necessary so that students could figure out how to solve the problem themselves.

Other teachers share Meyer's concern about Khan Academy's lack of context. Both Patel and Donahue plan to add a project component to their classes, where students can watch Khan's videos to learn certain skills and then use them to answer practical questions.

Meyer doesn't think Khan should be used in class to replace a teacher. Unlike having a teacher in the room, Khan's videos cannot make eye contact with students, pause and answer questions, or have a relationship with students. Still, he sees the benefit of Khan Academy as a supplementary tool in math classes if a student misses a day of school or needs extra help with a certain topic. He also believes that it would be helpful in situations where high-quality teachers are not available.

Patel agrees: "This kind of stuff really levels the playing field in bad schools where teachers aren't good or if students have a bad home environment. If teachers can teach kids to learn by themselves, the possibilities are limitless with online learning."