Educational achievement has traditionally been closely associated with general cognitive ability (g). Although g explains a substantial portion of variance in educational attainment, several non-cognitive factors have been found to relate to achievement beyond g. The present thesis focuses on exploring the association between achievement and two such factors: motivation and anxiety. The five empirical chapters included in the present thesis address several questions regarding the relation between motivation, anxiety and achievement, which to date remained unexplored. The present thesis includes data from two samples: the Twins Early Development Study (TEDS), a large-scale developmental twin sample from the United Kingdom (UK), and a sample of students attending the first year of secondary school in the UK, who contributed data longitudinally. The results showed that academic anxiety and motivation are domain-specific constructs. This observed domain-specificity of motivation and anxiety was also found to apply to their association with academic achievement. Motivation and anxiety constructs were moderately heritable, and the remaining variance explained by nonshared, individual specific, environmental influences. The cross-sectional and longitudinal links between motivation, anxiety and achievement were largely due to genetic influences common to all measures within a specific academic domain. The present thesis also explored the directionality of effects in the longitudinal associations between educational achievement and motivation; partly supporting the view of reciprocal links between the two constructs in several academic domains. However, a reciprocal relation between motivation and achievement was not observed in the domain of second language in a sample of naïve learners. The results of the present thesis have important implication for future research and practice. For example, it is argued that future interventions aimed at reducing the academic anxiety should consider three main factors: (1) its domain specific; (2) the directionality of effects in its association with achievement; (3) possible factors moderating or mediating the association between anxiety and achievement (i.e. motivation)
