The aim of the research conducted in the framework of this paper is twofold. In particular, the paper examines to what extent intelligence, personality traits and professional interests contribute to the explanation of the school achievement variance of upper primary school students on the one hand and to the school achievement in the specific group of school subjects (verbal-communicational, scientific, social-humanistic, technical and artistic group) on the other hand. In addition, an empirical analysis examining the incremental validity of personality traits and professional interests above and beyond ability effects was conducted. A total of 263 pupils from eighth grade of Vladimir Gortan Elementary School in Rijeka participated in this research. 128 examinees are male and 135 are female. In order to investigate a predictive strength of intelligence, personality traits and professional interests in predicting both general and school achievements in the specific group of school subjects as criterion variables, several hierarchical regression analysis were conducted. The research results indicate that there is a significant and positive relationship between verbal, numeric and abstract abilities, as well as conscientiousness and investigative interests and general school achievement, including the achievements in all specific groups of school subjects. Moreover, regression analysis results have demonstrated that intelligence is a significant predictor for all school subjects groups. Also, the analysis confirmed personality traits as predictors of the achievement over and above intelligence in all school subject groups, except technical ones. Above and beyond intelligence and personality traits, professional interests explain an additional proportion of variance when criterion is both general school achievement and achievement in the specific group of school subjects. Research results within this paper highlight importance of examining the school achievements and emphasized the contribution of systematical analysis of pupils' success in the elementary educational system.