Stepwise regression with exact calculation as the dependent variable and non-symbolic comparison, non-symbolic estimation and non-symbolic addition as predictors, regressing out the effects of age, schooling, general intelligence and spelling abilities.

TA = typically achieving; MD = mathematical difficulties; w: internal Weber fraction; cv: coefficient of variation. Stepwise regression with exact calculation as the dependent variable and non-symbolic comparison, non-symbolic estimation and non-symbolic addition as predictors, regressing out the effects of age, schooling, general intelligence and spelling abilities.