Objective: The overarching goal of this study was to better understand the relationships physical activity (PA) and other physical well-being variables (i.e., body composition and fitness) have with mental health symptoms, academic achievement, and executive functioning in a middle-school aged sample. Additionally, this study sought to explore the unique contributions physical well-being variables and in particular physical activity had on youth and teacher- rated symptomatology. Finally, this study aimed to determine whether the relationship between PA and academic functioning was better accounted for directly or indirectly using a serial mediation model whereby PA predicted academic achievement through neuropsychological functioning and ADHD symptoms. Background: Previous research has revealed that youth who engage in physical activity, be it a one-time acute bout or an intervention, generally experience positive neuropsychological outcomes and in some studies, a decline in Attention-Deficit/Hyperactivity Impulsivity Disorder (ADHD) symptoms. Additionally, studies investigating the efficacy of physical activity in reducing depression and anxiety symptoms have produced promising findings. Furthermore, the relationship that increased physical activity has with academic success has been recognized for several years. Importantly, fewer studies have considered the relationship that everyday PA has with functioning using a cross-sectional design and hardly any studies have included youth ratings. Further, much of the research investigating this relationship has been completed with either community or clinical samples. When studies have involved school samples, they have excluded participants with elevated ADHD symptomatology and considered the relationship fitness, rather than PA, has with academics. Finally, while a large literature suggests that PA can contribute to improvements in academic achievement in typically developing children, there is limited information on whether this relationship occurs in the context of ADHD symptoms. Method: 59 youth enrolled at a local middle school and six youth attending a day camp completed questionnaires, tasks of neuropsychological functioning, and measures of body composition during a one-hour period. Further, for students, their elective course teacher completed a rating scale yielding scores for inattention and hyperactivity/impulsivity symptoms and scores from the Alabama Physical Fitness Assessment were retrieved. Results: There was a positive relationship between self-reported PA and self-reported academic achievement, and a negative relationship between self-reported PA and internalizing problems. Regressions showed that physical well-being variables accounted for a unique portion of the variance when predicting youth-reported internalizing problems. Notably, this relationship held when controlling for demographic variables and task-measured neuropsychological functioning but not when self-reported executive functioning was included in regression models. Mediation analyses revealed significant direct effects between self-reported PA and self-reported academic achievement but did not identify any statistically significant indirect effects. Conclusions: The findings in this study support the research suggesting that higher levels of PA are associated with better academic performance and fewer internalizing problems. While significant relationships between PA and attention difficulties did not emerge the results still highlight the importance of physical activity to overall well-being and encourage continued research on the topic of physical activity, mental health, and domains of functioning.