Introduction: Attention Deficit Hyperactivity Disorder (ADHD) is a complex neurodevelopmental disorder with numerous hypothesized risk factors that have not yet been thoroughly investigated in many non-Western populations, including Mongolian schoolchildren. Exploring these risk factors could yield insight on which children are more likely to be impacted and on how risk differs across locations and cultures. Objective: The aim of the study was to assess whether elevated scores reported by parents and teachers on the Conners-3 Assessment, a detailed survey tool used to assess ADHD symptoms, correspond with indicators of lower socioeconomic status. Methods: We conducted a cross-sectional analysis involving 201 schoolchildren aged 8 to 13 attending a public school in Ulaanbaatar, Mongolia. We investigated associations between factors including student age, parental education level, family income, exposure to cigarette smoke, calcium intake and vitamin D status with Conners-3 scores for inattention, hyperactivity, and defiance/aggression. Cohen's d effect sizes and adjusted mean differences (aMD) for Conners-3 scores between groups were calculated using multivariable analysis. Results: Our findings revealed large effect sizes between different types of accommodation, a key indicator of socioeconomic status in modern Mongolia, and moderate effect sizes between different levels of parental education. Other findings included that engaging in over 2 hr of outdoor activity was independently associated with an increased inattention score (aMD 0.53, 95% CI [0.03, 1.03]) and increased hyperactivity score (aMD 0.63, 95% CI [0.10, 1.16]). A lower household income was independently associated with an increased inattention score (aMD 0.0005, 95% CI [0.000011, 0.001042]) and increased defiance/aggression score (aMD 0.0009, 95% CI [0.0004, 0.0015]). Factors such as calcium intake, Vitamin D level, exposure to cigarette smoke, and parental employment status did not yield significant associations. Conclusion: We found that Conners-3 scores indicating higher symptoms of ADHD among Mongolian schoolchildren were associated with lower household income and high outdoor activity, and should be further investigated in relation to type of accommodation.