It isn't just that the level of education of this school is high. It's that it's also

A. The level of education in this school, which is usually quite high, shows only slight variations from year to year.

B. The standard of education is not high in this school, but at least all the students are at the same level.

C. Not only are the standards of education good in this school, but it has also maintained those standards over the years.

D. It isn't fair to deny that this school is successful, as it has had the same high standards for many years now