This paper discusses the impact of orthographic manuals on the state of literacy, i.e. the relation of orthographic literacy and orthographic standardisation. The established hypothesis claims that frequent changes of orthographic rules during the pupils’ primary and secondary education do not have any considerable impact on their orthographic habits. In other words, the quantity of orthographic mistakes observed during a longer period of time and in conditions of changed orthographic rules would not show significant oscillations in their spelling. In order to confirm the hypothesis, a questionnaire was conducted encompassing 41 tests among 526 students of a technical study programme during four consecutive academic years, pursuant to whose results a writing uniformity index and a categorisation of orthographic controversy into six classes is established. The Croatian language has been selected for the observation due to multiple orthographic changes in the last 30 years in the three major orthographic points: writing of the covered r, writing of d and t in front of c and č in declination of words ending in -tak, -tac, -dak and -dac, and the issue of compound or separate spelling of the negation particle and the auxiliary biti (to be). Moreover, the paper methodologically and quantitatively establishes criteria according to which the second established hypothesis on evolutionary orthographic literacy can be confirmed. The conclusions are expected to be able to contribute to the better understanding of orthographic planning and application of orthographic norms in schools.