The purpose of this paper was to investigate the relationship between the implicit and explicit language knowledge at children of lower levels of primary school. The main goal was to determine whether there is a balance between the implicit and explicit knowledge of the spelling rules by lower level primary school pupils. It was also important to explore how students apply the knowledge gained in the subject the Croatian language to other subjects (in this case - Nature and Society). The research sought to establish the link between the knowledge of spelling rules (explicit knowledge) and their usage in writing (implicit knowledge) in the final year of lower level of the primary school (grade 4). The research participants were 80 pupils of four fourth grades of the Eugen Kumiĉić Primary School in Velika Gorica - 43 girls and 37 boys. The research instrument was designed for this study and it had a form of teaching material in which students need to write target words using the correct spelling. The important research finding is that pupils are more familiar with the examples they have encountered in the subject of the Croatian language than those of Nature and Society. That proves the hypothesis that the teaching content of the two subjects are not interrelated to a great extent. It has also been found that there is no balance in the implicit and explicit spelling knowledge in students of the fourth grade. From the results of the research it can be concluded that, regardless of continuous learning and the acquisition of spelling norms, the implicit and explicit knowledge of students is still uneven.