Abstract: The study determined the effects of single parent on academic achievement of secondary school students in Ibadan South-East local government Area of Oyo State, Nigeria. The whole of secondary school students in Oyo state represent the sample population. In carrying out the study, ex-post facto or causal survey design was adopted for the study. Stratified proportional random sampling technique was used in selecting the subjects used for the study. The reliability and validity of the instruments were determined before use by the investigators. The study revealed among other things that: There is no significant difference between students from divorced home and their academic achievement. There is no significant difference between children in step- families and their level of academic achievement. There is no significant difference between academic achievement of students from single-parent and their counterparts living-together parents. There is no significant difference between the academic performance of students from favourable home environment and their counterparts from unfavourable home environment. The following are included in the recommendations in the study. The husband and wife should be made to realize that it is their joint responsibilities that can see their children through their educational achievement. Class and subject teachers should be sensitive to significant changes in any student behaviour and attitudes. The school should ensure that information on the child`s home circumstances is regularly checked and up dated in conjunction with the parents.