Jane says the extra attention is the key to their success.
Helen, 16, a pianist, is now at a music school in Edinburgh. To qualify for the place, she learned to play the bassoon from scratch as a second instrument during the six months building up to her GCSEs.
Mrs Lowe, from Welwyn Garden City, Herts, is qualified as an English teacher.
She said: "The main advantage is the amount of on-to-one contact the children get. They ask hundreds of questions a day sometimes. They can't do that in class because they have to wait their turn. By the time they get the chance, the moment has gone.
"When Helen was taking her GCSEs, she had a problem with algebraic fractions, which I wasn't able to help with. We just popped in on a friend who was able to sort it out on the way to the exam.
"There are about 40 to 50 families like us within half an hour's drive of where we live.
"My husband works in computers and there is better computer equipment at home than most schools would have."