Not A Teacher
"At School" would refer to the education of the person in question before he went to Cambridge University. This could the a state or public ( the name used for a private fee paying school in the UK) schools that he would have attended until he was 18 years of age.
In the UK we would normally describe someone as studying or reading Classics at Cambridge.
It should also be mentioned that in the UK we would normally write 'specialised' rather than 'specialized' which is the AmE spelling another example would be fuse rather than fuze.