There is now strong evidence from many different studies that the greater part of variation in IQ, in western white societies at least, is genetically determined. The evidence for educational achievement is based on fewer studies and is more conflicting. In this paper we detect and estimate genetic components of performance in the dijl" erept J~ llbjects of a school examination and then seek to discover whether these components are all measures of the same general ability or whether they also include variance due to independently inherited specific abilities.