With the support of West Sussex County Council, the school has implemented a raft of measures designed to raise the achievement of all its pupils, using data to monitor individual progress and ensure that pupils are not performing below their ability level.
Peter Thomas says: "I like context-specific approaches. Our job is to know what our pupils are capable of. That requires data and appropriate structures so that we can 'interfere' where necessary."
In science, for instance, Tanbridge House boys outperform girls by a small margin, and the school wanted to raise achievement all round. Three years ago, Brian Arden, the head of science, designed a monitoring system which uses pupil scores in key stage 3 science curriculum tests to set targets for their performance in tests during the following year. Each term he produces a bar chart that indicates at a glance which pupils in each class are overachieving or underachieving, and shows the "value added" to theirperformance.
Pupils with a minus "value added" score - the brightest pupils can also be the laziest, says Brian Arden - are then targeted by science staff. A pupil may simply need to be encouraged to improve; in other cases, a stern letter may be sent to their parents.
"Often it turns out that it is the boys who are underachieving," says Brian Arden, "but this system is not detrimental to girls, and we know that we are putting the extra effort into the individuals who need it."
Ken Vose, the school curriculum manager, produces termly a performance review which gives pupils a grade for achievement in each subject, based on their term's work and a mark for effort (where one means excellent, four means very poor). More than five grade ones for effort brings a reward, while a four means a target for improvement must be set with the teacher.
Parents like the system, he says, and so do the pupils, particularly the boys. Teachers find that it helps motivation, as pupils are anxious not to get a grade four.
"It does take a lot of computer time," says Ken Vose, "but I believe this is the right sort of monitoring."
Lesley Cooke, head of one of the school's three houses, arranges meetings with parents and pupils in cases where pupils - all of them boys, to date - are scoring too many threes or fours for effort. They then set targets together.
"If you can involve parents more and show them how they can support their children, you're on to a winner," she says, and reports that parents contact her much more readily now to discuss problems.
In the past three years, boys' results at Tanbridge House school have improved by 15 per cent, which Peter Thomas attributes largely to the effectiveness of these tracking systems.
Ken Vose adds: "It's better to say that boys' performance is not as good as it should be than to say that girls are doing better than boys. Rather than say to the boys, 'You've got to be as good as the girls', we need to be able to say to an individual, 'Here's a subject where you need to improve'."