Just as a person faces difficulties in acquiring and mastering different skills, mastering a language - especially a standard idiom - is no exception. The native idiom is adopted easily and without struggle, which is not the case with the Croatian standard language. Although the teaching of the Croatian language in schools is largely oriented towards practicing and adopting the morphological norm, deviations from the morphological norm are constant and appear at all educational levels. In order to reduce these deviations, it is necessary to study them as well as try to prove why certain morphological deviations occur. Some deviations have been noted for many years, and researchers are trying to figure out if they are to a large extent the result of the influence of immanent grammar and whether they change with age, as well as the detection of other influences. This thesis will analyze the deviations from the morphological norm among older students of one elementary school in the Karlovac County. The basic task is to use a questionnaire to examine the knowledge of the morphological norm, and then to assess whether the obtained results are a consequence of the echo of immanent grammar and whether morphological deviations decrease with an increase in the level of formal education. In order for deviations from the morphological norm, and the norm in general, to appear as rarely as possible, it is necessary to improve the ways and forms of teaching normative grammar and to point out the necessity of language-communicative competence, which is best developed through a standard idiom.