The main idea behind single-sex schooling is to reduce the interaction with the opposite sex for better academic, social and emotional development in a belief that this safe environment will eliminate destruction arrived created from opposite-sex classmates. In fact, single-sex schooling results in a decrease in the likelihood of attending the party and having romantic relationships at adolescence (Cardona, Kaufmann, 2017). But, does this perpetuate better outcomes in the short and long run for participants of this schooling type is an abiding interest in many studies? Debates over the pros and cons of single-sex schooling are widespread and some papers are taking an ideological stand, and holding upon polarizing views (Gordillo, 2017). Gordillo (2017) analyzed some meta-analysis studies and found that these papers did not include valuable research papers with opposing findings which give doubtful conclusions. Most of the existing studies evaluated the academic attainment of single-sex school students and comparative analyses are done to cross-analyze with coeducational students' achievement. This paper, on another hand, focuses on how single-sex school graduates find it challenging their relationship with the opposite sex in mixed-sex spaces in the post-school period. This study particularly focused upon challenges in relationships with individuals of the opposite sex at university, work-space and with the spouse. The study is taken place at Kazakhstan's educational foundations which run both single-sex and coeducational schools. Findings reveal graduates of single-sex schools have not faced significant challenges in relationships with the opposite sex at university, work-space, and spouse compared to coeducational school graduates.