Today, the learning and teaching process in schools is increasingly being conducted with the help of digital technologies, using various applications and content. The selection and implementation of these tools depend on the teachers’ competencies and the technological equipment of the classrooms or educational environment. Teachers acquire ICT skills and competencies during their studies and as a part of lifelong learning. Modern education involves integrating ICT with teaching methods and strategies in an interesting and creative way for learners, to ensure effective and meaningful knowledge acquisition. This thesis describes the process of designing digital content in the form of a multimedia instructional message, for the subject Mathematics for the 1st, 2nd and 3rd grades of elementary school, in accordance with the principles of the Cognitive Theory of Multimedia Learning: multimedia principle, spatial contiguity principle, temporal contiguity principle, coherence principle, modality principle, redundancy principle, signaling principle, individual differences principle, animation and interactivity principle (Mayer, 2001, 2005, 2009, 2014). As part of this thesis, research was conducted to test the effectiveness of a multimedia instructional message for repetition and acquisition of basic mathematical concepts. The research was conducted on a sample of 17 learners from 2nd grade of Davorin Trstenjak Elementary School in Zagreb. The results showed an insufficient level of prior knowledge of the learners in Mathematics for the 1st and 2nd grade of elementary school, which negatively affected the retention and understanding of the presented mathematical content for the 3rd grade of elementary school. Although the digital teaching content was developed according to empirically established principles of cognitive theories in the field of multimedia, it was shown that it cannot completely replace the subject environment and compensate for the insufficient level of prior knowledge of learners. However, it can encourage, motivate and inspire them in the process of acquiring knowledge.