Communication in the mother tongue is the first of eight key competences defined by the European Commission in the document called The European Reference Framework of Key Competences for Lifelong Learning therefore it is important to know the ways to develop and encourage language competences (Pavličević-Franić, 2007.). While growing up, children adopt language spontaneously even though we know mastering a language is a long-term process. In their early childhood they first acquire the mother tongue through their environment, but after starting school, along with their organic idiom, it is expected they start to master the standard language. Furthermore, during this period children encounter the idioms of their peers, as well as the possible learning of a second language. One of the most prominent aims of Croatian language teaching is developing competences necessary for successful verbal communication, which applies to all school subjects, not only Croatian language. The success of this process enables easier mastering of educational content, readiness to communicate and overcoming everyday difficulties. Because of that pupils should be encouraged to use their vernacular and dialect, and not only the standard, because it is a part of the Croatian cultural heritage, as well as their identities. The unstoppable progress of technology today leads to the growing presence of Anglicisms that school age children use in their vocabulary much more frequently. For the purpose of this thesis, the diversity of lexical idioms in the verbal expression of primary school students was researched. With the main aim, three problems were introduced: questioning the lexical diversity, questioning the presence of the vernacular and the presence of loanwords. From the aim and the problems of the research, also set were the three hypothesis which were meant to examine if the lexical diversity was in line with the students’ age, do the students use the particularities of their vernaculars and if they used loanwords. The research was conducted in Zagreb and the participants were third and fourth grade students from the same primary school. The results showed that the lexical diversity is not in line with the age of the students. However, two hypotheses were confirmed; the students do use the particularities of their vernaculars and they do use loanwords, out of which most are Anglicisms.