Sentence:  Imagine a country where children do nothing but play until they start compulsory schooling at age seven. Then, without exception, they attend comprehensives until the age of 16. Charging school fees is illegal, and so is sorting pupils into <WSD>ability</WSD> groups by streaming or setting. 
Meaning of the word marked with <WSD> tags:  The quality or state of being able; capacity to do or of doing something; having the necessary power. (First attested from around (1350 to 1470).)<ref name=SOED/>