For pound;9.99 an hour, the service provides tuition via the internet in one-hour sessions, day and night.
Teenagers take a test to find out their ability. Then Tutor Vista, the company behind the scheme, arranges a session with a tutor.
Pupils can communicate by headphones and microphone, and work through exercises, inputting their answers via an electronic tablet. On the other end of the line are a team of 50 Indian graduates, all with degrees in the subject they teach, and teaching certificates.
Some 450 parents have signed up to Tutor Vista, which aims to prepare pupils for national tests and 21 GCSEs and A-level subjects, since it launched two months ago. It was unveiled in the US in November.
The firm now has plans to expand into schools. Martin Baker, the firm's UK manager, said: "Pupils could be on the computer being given a multitude of different lessons. And gifted and talented children could be assigned more advanced work without disrupting the lesson for others."
He said it was good value as UK private tutors could charge more than pound;20 an hour. The Indian tutors were all very familiar with the courses they taught, he said, and the quality of the technology meant conversations were clearer than by telephone.
However, John Bangs, National Union of Teachers' head of education, said he remained sceptical about virtual teaching.
"My advice is to be very, very careful with online tutoring, mainly because the tutor does not know the teaching the pupil has received from their school. It cannot be a substitute for face-to-face teaching," he said.