During the project “Development of Communicative Competence in the Early Croatian Language Discourse”, a research on the mastering of Croatian as a second language was carried out among the children of Croatian emigrants to Germany. It needs to be stressed that the participants start learning Croatian systematically only within the program of the Croatian tuition abroad, when they encounter the standard Croatian idiom which is more or less different than their local Croatian idiom which the speakers were exposed to in their families. The input language is the individual organic idiom of the Croatian language, while the target language refers to the standard Croatian language. The process of the acquisition of the organic or first language (L1) differs from the process of the other or second language (L2) learning. This is due to the fact that in the process of the non-mother tongue mastering an interlanguage is created in which elements of the first and the second language interfere. In this process non-mother tongue learning can have a double meaning: learning a completely new and unfamiliar language system (foreign language), or acquiring a language idiom which the speakers had already partially mastered, usually in the early childhood. In that case we speak of the heritage language, the language of their parents, their cultural circle, and their national identity. Although all pupils who participated in this research had been born in the Federal Republic of Germany and have the German language as their dominant idiom, most of them consider Croatian to be their mother tongue. However, this research and the communicative practice have confirmed that the German language competence of the participants is higher than their Croatian language competence. Despite their personal attitudes towards Croatian as their mother tongue, the truth is that they learn Croatian as special kind of second language (heritage). The paper brings out the results of 150 pupils participated in the research, ranging from 6-18 years of age, and attending Croatian classes abroad in the German province Baden-Wurttenberg. A test of communicative competence was conducted and the written works of pupils were analyzed in order to examine their language competences in grammatical and lexical level of the Croatian language, according to age, cognitive development, communication, language exposure and language foreknowledge. The analysis of questionnaires was to determined the attitudes of pupils and teachers in Croatian tuition abroad (motivation, purpose and learning needs, socio-cultural environment ).The data were analyzed with the SPSS statistical analysis software. The method used was Pearson’s correlation coefficients to show correlation between the dependent variable (mastery of the language competences) and the independent variable (years they had spent learning Croatian). The Mean value, standard deviation, median-central value, and minimal and maximal score were used in the description and comparison of deviations from the standard language norm. Kolmogorov Smirnov z test was used to test the normal distribution, Kruskal Wallis test for differences between the different age groups of students and teachers, and the Mann Whitney test was used to assess the differences in the attitudes of teachers with regard to the degree and gender. Research results will be used for the analysis of language competences in pupils whose second (heritage) language is Croatian and for assessing the level of acqusition of Croatian language teaching abroad.