Motivation theories are often used in educational research to explain students‟ choices, and performance in school activities. Alienated or disaffected students generally lack motivation to attend school and to engage in learning. Achievement Goal Theory is a motivational theory focusing on the criteria or standards of excellence that individuals use to evaluate their competence (Meece, Anderman, & Anderman, 2006). According to Nicholls (1989), children after the age of 10 to 11 years develop at least two different ways to evaluate their ability. However, there are questions about “what happens in younger ages and specifically at preschool age?” and “how these ways of thinking are being developed?”The present thesis examined the above questions in relation with the phenomenon of competition in preschool aged children (4-6 years old). This is because competition is a daily phenomenon in educational environments (Shields & Bredemeier, 2009) even in kindergartens (Sheridan & Williams, 2006).In Chapter II, a literature review summarizes relative studies devoted to competition, the main characteristics of the preschool age and the factors which affect competitive behavior. Furthermore, theories of motivation, children‟s perception of their ability, children‟s perceptions of learning environment and the correlation between them are summarized. The main results of the literature review showed that competition is a daily phenomenon in educational settings. From the age of 4 years old, children perceive competition and present competitive behavior trying to excel among peers. The factors which affect the expression of competitive behaviors are: a) age, b) gender, c) composition of the team. According to Achievement Goal Theory the motivation of children is affected by how they evaluate their ability. The learning environment, which can be distinguished in mastery environment and performance environment, affects the way children perceive their ability.Three distinct studies have been carried out and their results are presented and discussed in Chapters IV-VI, aiming at: i) examining the ways through which preschool children express competitive behavior in kindergarten classroom, ii) developing a direct observational system which aimed at assessing competitive behaviors in preschool children and iii) examining how competition, in a learning environment, affects children‟s perception of their performance.The data obtained are presented and thoroughly discussed in Chapter VII, while the general conclusions and the future perspectives are presented in Chapter VIII. The main findings of this thesis can be summarized below. It was showed that preschool children express competitive behaviors both verbally and physically in kindergarten classrooms. More specifically, these behaviors appear with higher frequency during organized activities. It was also found that competition may affect preschool children‟s performance but not their perception of performance. Finally, in order to encourage preschool children‟s motivation for learning, some helpful advices for kindergarten teachers are presented in the Chapter IX.