There are many studies on the relationship between academic self-efficacy and academic performance; however, there has not been a moderation analysis performed on the impact of carelessness/insufficient effort (C/IE) on the relationship between academic self-efficacy and perceived academic performance. A total of 731 adolescents school children (Lima, Peru) from a public educational institution participated. Two moderators were used, namely the sex and age of participants, and a sensitivity analysis was performed using both clean and dirty C/IE data. The prevalence of C/IE was 14.3% of the possible cases. The interaction between self-efficacy and age was affected, while the main effect of self-efficacy remained strong. It is concluded that the effect of moderators changes only slightly when their effect size is not weak.