They do not have special lessons as such but meet once a month after school - rising to once a week in their third year - to learn study skills and take on extra work they would not be able to do in a whole-ability class, a recent example being chromatography inchemistry.
Perhaps Mrs Thatcher (a second inchemistry from Oxford) was right when she observed that all a first-class mind allowed a man to do was to see every problem from every angle without coming to any hard decisions.