The media plays a major role in an individual's life, and their ubiquity has increased through the process of globalisation. Modern technological advances have formed a culture of screens that affects the lives of all individuals today. Media in themselves are neither good nor bad, their influence depends on their way and time of use, and the general knowledge is that children and young people are increasingly and daily using different modern media. It is known from the literature that the media positively influences children's development, understanding of global themes, and promoting cultural diversity. A negative impact occurs when the media is used too often, for inappropriate purposes, and when it is used inconsistently with the child's age. For these reasons, this thesis was intended to investigate the positive and negative effects of digital media (DM) on children's behaviour and development. The participants in the study were classroom teachers and students of various teachers' studies in the Republic of Croatia (N = 190). In the absence of standardized questionnaires and scales, a scale of positive and negative effects of digital media on children's behaviour and development was constructed. The scale particles were produced on the basis of a study of recent literature on this subject, and three experts in the field of school psychology and pedagogy worked on the particulate matter proposal. Two factors were extracted by factor analysis (Max likelihood factors method): 1) negative effects of DM on children's behaviour and development; and 2) positive effects of DM on children's behaviour and development. Both of these factors are of satisfactory reliability (Cronbach Alphe for both subscales are high), and some of the particles are also in statistically significant positive correlations with some socio-demographic variables (teacher education level, motivation and frequency of DM use in teaching). The newly completed scale has been used in this research and it is recommended to use it in further research. Research results show that teachers and students statistically significantly evaluate the negative effects of DM over the positive effects of DM on children's behaviour and development.