The sex is one of the significant factors of interindividual variability. In most of the morphological characteristics, sexual dimorphism is not expressed before puberty, but with hormone changes leading to sexual maturity, some differences start developing, including different sport efficiency. This transversal research has the purpose of determining sexual differentiations of morphological characteristics and motor abilities in students from the fifth to the eighth grade of elementary school and to identify structural differences between the sexes: 453 boys and 567 girls. In kinesiology, we study and note changes caused by growth and development, thus this research, with as many as 1020 subjects in the period of crucial changes caused by sexual maturity, will study the differences between morphological characteristics and motor abilities in students and identify the significance of differences based on the sex. To solve this issue, we need to define and compare the factors responsible for biomotor development in children of a certain sex, ages 11 to 14, as well as quantitative sexual differences in morphological characteristics and motor abilities in relation to age. While establishing the actual state of the subjects, the biological acceleration phenomenon (secular trend) may be indicated, and for precise determination of morphological-motor status of students, it was necessary to choose a model for establishing the selection of variables. The sample of variables in this research will involve the total of 25 variables: 14 morphological measures and 11 motor measures calculated by 8 educated measurers, while the total selection of variables will be representative, precise, reliable and appropriate for the sample of subjects. Morphological measures have been selected in a way to cover hypothetically fourdimensioned morphological domain defined as: longitudinal dimensionality of skeleton, transversal dimensionality of skeleton, volume and body mass and sub-skin adipose tissue. The selection of variables to assess motor status was done in a way to assess even latent motor dimensions, and in order to achieve this, the suggested battery of tests for following and evaluating motor abilities in elementary school students has been added five additional motor tests. In order to generate methodologically correct and interpretable scientific conclusions from the obtained data, certain appropriate data processing methods have been applied, and for statistical processing we used Statistica for Windows 8.0 software package. The reliability of anthropometrical measuring and motor testing is entirely satisfactory and the obtained variables can be fully trusted, there are no statistically significant differences in variables distributions which might significantly harm the conception of distribution normality and the selection of data processing methods completely satisfies the demands of the set issue, hypotheses and the aims of research. The research identified sexual differentiations of morphological and motor development in school children ages 11 to 14 and determined the differences in development and /or integral function with regard to the sex. Differential sex differences in the structure of morphological parameters evidently exist and their basis have different time, i.e. periodic, involvement of development stages. At the age of 11, the advanced pre-puberty period is clearly evident in girls, followed by puberty. At the age of 12, girls reach the puberty swing, which is evident in the further development of bicrystal diameter and longitudinal dimensionality of skeleton, primarily in lower extremities. In boys, the puberty swing comes at the age of 13 which is evident from the development of longitudinal dimensionality, and less from the transversal dimensionality of the skeleton. Secondary discriminant characteristic can be continually noticed in all the variables for assessment of the dimension of accumulating adipose tissue reserves, and absolute values of sub-skin adipose tissue are more expressed in female students. Indicatively, secondary determinants of distinguishing the groups of children by the sex is still sub-skin adipose tissue accumulation in a way that girls constantly display this dimension more evidently. In all four age categories, we established a statistically significant difference between boys and girls in the performance of applied motor tests. In younger age groups (11 and 12 years old), girls are more superior than boys in flexibility manifested in the larger movement scope in a certain joint or a set of joints, i.e. in joint mobility, as well as in the lightness and gracefulness of movements. Motor efficiency in boys compared to girls is evident in the greater power of trunk, greater explosive power of jump and sprint type as well as in coordination. In older age groups (13 and 14 year old), differences in flexibility are more expressed on behalf of girls, which enables them the realisation of movements with larger amplitudes. In boys, the difference in explosive power is increased, particularly of throwing type with better agility, balance and greater static power of arms and shoulder belt. Evidently the development of muscle mass is more increased in male than in female sex. Sexual differentiations are significantly more expressed in puberty than in prepuberty stage which proves that the trend of development of certain motor abilities is different with regard to the sex, with the exception of psychomotor speed development. The obtained results have justified the set research issue since it was possible to determine and analyse the differences of morphological characteristics and motor abilities with regard to the sex in the developmental stages of pre-puberty and puberty. The set goals of study have been realised to a full extent, and the obtained results, their interpretation and stated conclusions give the answers to them. The set hypotheses of this research have been confirmed. The obtained results indicate that there are significant differences between sexes in morphological characteristics and motor abilities in a certain developmental stage of pre-puberty and puberty, both qualitative and quantitative. Based on the obtained results of the study, it may be concluded that morphological and motor development happens faster, i.e. sooner in girls compared to boys and that puberty swing happens in girls at the age of twelve (6th grade) and in boys at the age of thirteen (7th grade).