Sitting on the floor on a mild October Tuesday, 2-year-old Aileigh Mulligan happily sorts through the pieces of a ''Cooties'' game. Nearby, her 8-year-old brother, Liam, sits at a computer, hard at work on his fifth-grade math.

Liam's mom, Marcie Mulligan, gets some cereal for the toddler as she checks on a tank of half-transformed tadpoles for an upcoming study unit on metamorphosis. As she makes sandwiches for the family's lunch, Liam learns about the history of the ''Star Spangled Banner'' from ''Brain Pop,'' an online site that shows educational videos.

It's a typical day in Liam's virtual ''classroom'' in the family's comfortable Bethlehem home. Liam is the third of four children in his family to attend a cyber charter school and one of 1,850 students enrolled in Commonwealth Connections Academy, one of the 12 cyber charter schools statewide.

Nationally, Pennsylvania is regarded as a leader in the development of online charter schools. The state's first ''brick and mortar'' charter school opened in 1997, and its first cyber charter school a year later.

Cyber charter schools have had their share of controversy, particularly concerning funding. One of the earliest cyber charter schools in Bucks County ran into financial problems and lost its charter, forcing students to return to a brick and mortar public school. The highly publicized failure of the school prompted the state to tighten the law increasing accountability of charter schools.

Proponents say cyber charter schools offer benefits such as individualized instruction for students with special needs, time flexibility, increased involvement of parents and a more varied curriculum.

However, others claim students get less social interaction with teachers and other students, no access to specialized equipment for projects such as science experiments, and they can't participate in extracurricular activities, such as sports and marching band. It also places increased time demands on a guardian, who is required to be actively involved in the teaching process.

Like other charter schools, cyber charter schools are free and open to the public. Cyber school students use the same books and curriculum as traditional public schools use and have their progress monitored by teachers. However, since the student does the work from home via computer, more responsibility falls on the learning coach, usually a parent.

Dennis Tulli, CEO of Commonwealth Academy, says he had been a school superintendent of a brick and mortar school when he was asked to help start up the cyber school. ''I didn't like the idea of cyber schools,'' he says. ''I agreed because I believed you keep friends close, but you keep enemies closer.''

However, he soon began to realize cyber schools had a place in the educational landscape. ''Cyber schools are not for everyone,'' he says. ''But they meet the needs of a lot of children who can't be successful in a traditional setting. There is a place for both methods of delivery. We're not looking to close brick and mortar schools. This is just another option.''

Students who have enrolled in cyber school may be those with physical handicaps or learning disabilities, those involved in intensive training in a specialty, such as gymnastics, or those with parents whose work requires them to travel frequently. Tulli says 25 to 30 percent of the students enrolled in Commonwealth Academy previously were home-schooled.

Mulligan was home schooling her oldest son, Ryan, who was born with spina bifida, before the first cyber school was established. ''He needed a lot of physical therapy, and if he was in public school, it would've been hard to fit it in,'' she says. She enrolled him in cyber school in sixth grade and ''he loved it,'' she says.

''With home school, I was the end all and be all,'' she says. ''But here there are teachers correcting students tests and writing assignments. It's like home school with support. If I'm doing a lesson, I can call a teacher on the telephone and ask, 'How do you do this?'''

According to Tulli, when the school opened in 2002, there were 400 students statewide. ''We wondered if it would catch on,'' he says.

Now the 12 cyber charter schools in Pennsylvania' serve more than 16,000 students and Tulli anticipates the Commonwealth Academy will have enrollment of 2,000 students by the end of the year.

Things have changed significantly since Einstein Academy was chartered in 2001 by the Morrisville School District in Bucks County. The school, which once enrolled 3,000 students, became embroiled in controversy after it failed to deliver promised computers to students and had its Internet service suddenly turned off because of outstanding bills. The school lost its charter in 2003.

In response, the Pennsylvania School Boards Association filed a lawsuit in 2001 challenging the legality of cyber charter schools.

The following year, Pennsylvania updated the charter school law that previously had allowed school districts to issue charters for cyber school. Now, only the state Department of Education can grant these charters. The new law also verified the legality of cyber charter schools and called for an annual financial and academic assessment of the schools by the state.

''Cyber charter schools have been around long enough that they're no longer considered an experiment,'' says Andy LeFevre, director of Reach Foundation, a Pennsylvania coalition that supports school choice. ''The greatest accountability is by parent's choice. If parents are not happy, they can take their children out of the school, and what we're seeing by the growth in numbers of cyber charter schools is it's an option that's working for many families.''

Nationwide, charter schools have been booming. There are 4,224 charter schools in 40 states and of those, 242 are cyber charter schools, according to the Center for Education Reform, a nonprofit organization that researches education reform issues.

When a student enrolls in a cyber school, the cyber school gets the student's record from the student's home school and provides the student, free of charge, with books, curriculum, a computer, printer and high-speed Internet service.

Tulli says students are required to log on a minimum of 30 hours a week and the students' work is checked by the learning coach, as well as the teachers. Once a month, the student must mail in a portfolio of work.

Students take part in live interactive classes with teachers online, and if a student misses a live lesson, it is archived for later viewing.

Students have access to educational online services, such as ''Brain Pop'' and Discovery Education streaming videos. Each day, a student signs into his virtual classroom and gets his assignments for the day. If he falls behind, the teacher calls. Students receive quarterly report cards and are put on truancy if they don't do their work.

Mulligan says she has known students who were removed from the school for noncompliance. ''You're accountable for so many hours and so much curriculum,'' says Mulligan. ''It's not that easy. You're not just sitting in front of a computer.''

The curriculum includes hands-on science experiments, such as putting eggs in vinegar to see how osmosis works to dropping balls in flour to understand moon craters, says Mulligan.

In addition to the standard curriculum, cyber schools offer a wide variety of electives, from art to music to foreign languages. Because of the individualized curriculum, cyber charter schools have been an attractive alternative for children identified as gifted, as well as learning disabled.

''We can accelerate as many grades as a child needs,'' Tulli says.

Older students can even take college courses for credit and graduate high school with a college associate's degree.

Mulligan says Liam has some ''dyslexic tendencies'' and she is able to teach to his individual learning strengths. ''I'm not convinced he would do as well in a group setting,'' she says. ''If he doesn't understand, I can try a different angle. But if he was one of 32 kids, the teacher might miss that he's not getting it.''

She says Liam, who loves history, will finish his fifth-grade unit in December. He, then, will be able to start studying an elective or move ahead to the next grade level of history. "I think it's great you can explore an area you're interested in,'' Liam says.

One of the advantages of cyber school is its flexibility. Students can do work at night or on Saturdays and Sundays, if they have doctor's appointments or other commitments during the week.  Mulligan says her daughter, Jessica, who attended cyber school through fifth grade, would do lessons in advance to give herself an afternoon off.

Since students attend school at home, they get less socialization, so cyber charter schools have community coordinators who organize field trips. There also are group activities, such robotics club and Odyssey of the Mind teams.

''We don't have a football, basketball team or band, but we're going to have a great debate team next year,'' Tulli says.

Students also may take some community enrichment classes, such as gym, art or theater, that are reimbursed by the school.

Mulligan says Jessica chose to go to Nitschmann Middle School in the Bethlehem Area School District in sixth grade and had no problems with the transfer since cyber school uses the same curriculum as public school. Jessica now is involved in choir and the school musical and is maintaining a 4.25 average.

Ryan chose to attend Liberty High School in ninth grade and is in the marching band and drama club and is also maintaining a 4.25 average.

Mulligan says beside socialization, cyber students also miss out on group interaction in class.''There is a benefit to doing an oral report in front of 32 kids instead of just in front of mom and dad,'' she says. ''And we don't have access to petri dishes at home for science experiments.''

But Liam says he loves spending the time with his mother.  ''There's a lot of one-on-one,'' agrees Mulligan. ''But it's spent teaching, not playing games or baking cookies. The hardest part is balancing it. It's like a full-time job.''  The flip side is ''I love seeing wonder in his face when he gets it,'' she says. ''I love seeing him learn.''

Mulligan says she doesn't know if Aileigh will attend cyber charter school since the family approaches each year one at a time. ''The great thing is you have a choice,'' she says.