This chapter provides the associated literature and studies after the thorough and in-depth studies completed by means of the researchers. Peer is a person who is the same age or has the same social position or the same abilities as other people in a group or one that is of equal standing with another while a peer group, in sociology, is both a social group and a primary group of people who have similar interests (homophily), age, background, or social status. The members of this group are likely to influence the person’s beliefs and behavior. A definition by Merriam-Webster dictionary, Peer Pressure is a feeling that one must do the same things as other people of one’s age and social group in order to be liked or respected by them. According to Ryan (2000), a crucial component of interpersonal attraction and selection of peers is a similarity. Brown, Mounts, Lamborn, and Steinberg (1993) additionally recommended that adolescent peer group members choose each other based primarily on similar traits simply as adults do. it is unusual for a young individual to select a peer who uses cigarettes or alcohol in the event that they do not. Based on a recent study of the University of Maryland indicates that peer pressure begins earlier than previously thought. The researchers suggest that the group dynamics of childhood imply that conflicts between “group loyalty and fairness,” begin in grade school. Kids encounter peer pressure on an almost daily basis in school, as early as age 9. According to a study done by CREDE (Center for Research in Education, Diversity, and Excellence), peer groups are highly influential during early adolescence but that peers are less influential as kid’s get older. Peer Pressure “influences a person to alter his/her attitudes, values, behaviors, and relationship in order to meet the norms and values of the group” (Cho, 2012. p. 512). Responding to peer pressure is natural to humans. Adolescents were influenced to do things they thought they cannot do. In high school, teens are spending more than half of their time in the company of their peers (Updegraff et al. 2001). Teenagers, most likely senior high school students are very dependent on their friends specifically their classmates in school. They were influenced to do such things they don’t usually do. To mention with, engaging in a bad habit like smoking in order for them to fit in with their group. Though not all peer influence is bad. In fact, some peer groups influence students to do better and achieve in school. For example, intelligent students help their peers who are struggling to bring up their grades. (teens.love.to.know.com) “The catalog of settings where peers influence our decisions is large and varied, including our choices to engage in criminal behavior, smoke, perform charitable acts, follow styles and trends, educate ourselves, select a certain profession, adopt a new technology or buy a given product.” (Calv´o-Armengol and Jackson, 2009). According to Erikson (1968); Hartup (1983); Steinberg and Silverberg (1987), peer groups influence adolescent socialization and identity by allowing young persons to explore individual interests and uncertainties while retaining a sense of belonging and continuity within a group of friends. Thus, adolescents nowadays have a high curiosity that makes them want to discover new things that interest them with their peers. John Kirk’s study about the Peer Effect on Academic Achievement among Public Elementary School Students: A Report of the Heritage Center for Data Analysis, discusses the effects of peers and social interaction on academic achievement. It is stated that the data from the 1998 National Assessment of Educational Progress (NAEP) database on reading were used to test the influences of peer attitudes on academic achievement. The NAEP examines academic achievement in various fields. It is administered to students in 4th, 8th, and 12th grade. Results indicate that the peer effect is a strong influence on academic achievement, particularly in 4th grade. The significance of peer effect wanes by 8th grade. The Influence of Peer Group on Academic Performance of Secondary School Students in Ekiti State (B.Temitope, et.al., 2015), investigated the influence of peer group on the academic performance of secondary school students in Ekiti State. A total of 225 secondary school students have randomly selected from five mixed (boys and girls) secondary schools for participation in this study. The participants all responded to Peer Group and Adolescent’s Academic Performance (PGAAP) questionnaire. Data collected were analyzed and findings showed that peers age (young and old) does not influence academic performance of secondary school students. Gender (male or female) does not influence academic performance of secondary school students. Peers relationship influence academic performance of secondary school students. Peers pattern of socialization influence academic performance of secondary school students. Peers location influence their academic performance. Peers religion affiliation has no influence on the academic performance of secondary school students. Above results suggest that age, gender and religion difference does not matter in determining academic performance among secondary school students. The result further suggests that peers relationship, socialization, location, motivation and drug use have a great influence in determining academic performance of secondary school students. The study of “The effects of peer pressure on the educational achievement, educational aspirations and occupational aspirations of form four students in Kericho District” (R. Rono, 2012) dealt with the effects of peer pressure on academic achievement, educational aspirations and occupational aspirations of secondary school students. The study examined the relationship between the perception of peer pressure and academic achievement in a mock examination, peer pressure, and educational aspirations, and peer pressure and occupational aspirations. All subjects were administered a questionnaire comprising a section of open-ended items and a section of items utilizing a Likert scale. The Likert scale was used to elicit the subjects’ perceptions of peer pressure on various academic, educational and occupational issues. The results showed a statistically significant relationship between peer pressure and academic achievement when peer pressure to do homework and peer pressure to choose subjects were considered. No statistically significant relationship was obtained for the relationship between academic achievement and peer pressure to work hard for good marks and peer pressure not to miss classes. A statistically significant relationship was obtained between the perception of peer pressure and educational aspirations. The general conclusion emanating from this study was that first; peers exert some influence on the students’ decisions concerning academic activities and aspirational decisions. Secondly, the sex of the student determines the susceptibility to peer pressure in some areas while in other areas; sex does not make a difference. Thirdly, the type of school attended influences some aspects of academic and aspirational behavior while in others, there is no clear-cut influence. The researcher concludes that the effect of peer pressure largely depends on the issues concerned and the sex, school and residential status of the students i.e. it is significant in a short-term decision and not significant in long-term decisions.