Even the most academic schools have limits on how much time they can devote to an individual student. The reality of modern education is that all students matter and it is very important to a school's reputation that as many as possible get A-C grades. This can mean that very good students are supported less well than students who are achieving less than their potential.
Enrichment of most able students, or students aiming for very specific outcomes takes time, a lot of time and a lot of individual attention - things most schools cannot provide easily.
Some of our best work is with the most able students who want to aim for Oxbridge or a specific career but find the school is setting solo work that can seem quite boring and has little teacher involvement. We have the knowledge and expertise to support these students, complementing work at their school and giving time and understanding for the student. As we are also not part of the school environment we can develop a different more adult learning approach which would be difficult when the teacher is having to deal with a whole class and would be seen as having favourites.