This master's thesis explores one of the more prominent aspects of sports in elementary schools – aerobic endurance. Due to the sedentary nature of today’s lifestyle, children are becoming less and less endurable, which brings about an increased possibility of cardiovascular illnesses. Aerobic endurance is key for maintaining health. This functional capability also increases concentration, thus enabling an individual to stay concentrated for a longer period of time, as well as decreases stress, which is present even in the everyday lives of children. If teachers wish to develop endurance in children, they need to be familiar with its characteristics and the techniques of its development. The theoretical part of the thesis researches the field of endurance, aerobic endurance, and explores the main factors, which influence endurance. It presents methods of developing endurance and focuses on physical education curriculum in order to establish how it deals with aerobic endurance. The theoretical part also demonstrates and describes physical activities, additional elements and motivational procedures, which are important for a successful development of aerobic abilities in children attending second through fifth grades of elementary school. The aim of this master's thesis is to determine if age, gender and body mass index influences the aerobic abilities of children. Based on the theoretical aspects of this topic and the results of the practical part of the thesis, the aim of the thesis is to offer suggestions on how to develop endurance. The influence of age, gender and body mass index on aerobic abilities was determined with the help of a numerical value, which shows the maximum amount of oxygen an individual is capable of using during exercise and serves as the best indicator of an individual’s aerobic capabilities. This value is marked with an abbreviation Vo2max. For the purposes of this thesis, a Beep test was performed on a sample of 206 children, aged between seven and ten years old. A Beep test is a reliable and valid test for a VO2max calculation. The research showed that gender and body mass index influence the VO2max values, whereas age does not. Based on the ascertainment of the research and the received results, the determining values of aerobic capabilities were arranged on a scale to determine how many children have poor or very poor capabilities, according to their VO2max values. Such a research has not been carried out in a sample of young Slovenian children, which is why the results of this thesis could not be compared against any existing data. For the sample collected for this thesis, it was observed that 35% of the children have poor or very poor aerobic capabilities. The Discussion chapter presents the advantages of testing children for the purposes of determining aerobic capabilities in children from second to fifth grade and offers some pointers for developing aerobic capabilities of children. The physical education curriculum includes some possibilities of incorporating sports activities, which help develop aerobic capabilities; however, it is, for the most part, up to the teachers whether or not they wish to use them, whether or not they have the needed requirements to carry them out and the way in which these activities are organised in order to fulfil their intended goal. The latter can be achieved by forming homogeneous groups, selecting an appropriate sports activity and ensuring a proper amount of strain during exercise.