Social interaction and communication is basically orchestrated through Social Networking Sites (SNS) with Facebook being amongst the most popular ones. Previous research has shown users’ personality as a highly relevant factor when examining the way people behave virtually. In the present study, we investigated the relationship between Facebook usage and personality in children aged 10 to 13 years with a personal account on Facebook, defined in terms of a Five-Factor Model. The relationship between Facebook usage and users’ self-concept regarding their school performance and their happiness and satisfaction about life was also investigated. For this purpose, children’s teachers were asked to evaluate children’s school performance, in order to better examine the relationship between Facebook usage and users’ school performance. Three hundred and forty-eight (348) pupils of elementary and secondary schools in Patras (Greece) participated in the study. The results indicated that Facebook usage has a statistically significant association with personality traits like Neuroticism, Openness to Experience, Agreeableness, and Conscientiousness. Moreover, children who perceived themselves as good pupils did not have a Facebook account. Also, Facebook usage has been found to be negatively related to users’ school performance, as assessed by their teachers. No statistically significant associations were found between Facebook usage and users’ self-perceptions regarding their happiness and general satisfaction with life.