The objective of this thesis is to analyze one of the main aspects of children education in Brazil: age-degree delay. Chapter on shows that family factors have an influence in children education using the 1996´s national survey Pesquisa Nacional por Amostra de Domicílios (PNAD/IBGE) and its mobility supplement, which has some grandfathers and grandmother´s indicators. An income effect and a parent´s education effect in children schooling delay are identified using three instruments: parent´s school supply, permanent family factors and the 1971 educational reform. Per capita family income and parent´s education have a negative effect in the child´s probability of being behind at school. Probit and ordinary least squares (without considering endogeneity) results present evidence that there is an upward bias in the parent´s education coefficient and a downward bias in the family income coefficient. Chapter two analyzes the impact of child´s nutritional status in school entrance delay using the survey Pesquisa de Padrões de Vida (PPV/IBGE). We show that, controlling for family income and considering the endogeneity of nutritional status, children who have a better indicator of height for age, have a larger probability of going to school whit exactly 7 years of age. Chapter three studies the relationship between student´s proficiency in the 4th grade of primary education and student´s age dispersion in the class, using the survey Sistema de Avaliação de Educação Básica 2003 (SAEB/INEP-MEC) and a method to control for unobserved factors in school. We show that students in more heterogeneous classes in terms of student´s age have less proficiency. We also show that having a teacher with a pos- graduation level reduces the negative impact of age dispersion on student´s proficiency.