Nigerian adolescents are facing increasing rate of parental separation, which is affecting their overall development, including good mental health. Various studies have examined the impact of parental separation on the self-esteem of adolescents. Outcomes of such studies are elaborate, complex and intricate; hence the need for this inquiry. The present inquiry re-examined how parental separation influence in-school adolescents self-esteem in Ilorin, Nigeria. The model adopted for this research is descriptive survey, using stratified random selection procedure across six schools in Ilorin metropolis, with the purpose of re-considering how gender, age and school type moderate the impact that parental separation has on the self-esteem of the in-school adolescents. Copies of the adapted form of Rosenberg Self-Esteem scale were administered to 300 students from separated parents. The t-test and Analysis of Variance were used to analyse the hypotheses. It was discovered that about three-quarter (216 of 300) of the participants scored below 50 (have low self-esteem), thus parental detachment has effect on the self-esteem of both male and female in-school adolescents negatively. However, the influence that parental detachment has on in-school adolescents' self-esteem varies on the basis of age and school type.