Spain has become the country in the European Union with the fourth highest number of overweight and obese children. This condition directly affects physical health as well as mental health. The objective of this research study was to evaluate motivational aspects in one group of obese or overweight adolescents and another group of normal-weight adolescents. For this purpose a descriptive observational study was carried out in an educational institution in Guadix (Granada). The universe was composed of 200 children of ages 10 to 14. A sample of 24 children was selected by means of proportional random sampling with an error of 0.19, and was divided into the following groups (i) 12 normal-weight children; (ii) 12 obese children. Motivation was measured by means of the School Motivation Analysis Test (SMAT), a multidimensional measuring instrument based on Cattell's dynamic model of motivation and emotions. Our study evaluated five motivational parameters: TAO (total autism-optimism), TGI (total general information), TIN (total integration), TPI (total personal interest), and TCO (total conflict). Our results showed that for each of the SMAT variables, the overweight and obese children obtained an average value of 4.5 in contrast to the normal-weight children, who obtained an average value of 5.9. This indicates that overweight and obese children have low motivational states and a higher level of frustration. They also tend to distort reality by alleging the existence of obstacles that prevent them from achieving their goals.