Presented are the largest studies in the field of risk assessment of sexually abusive youths, of youth with low intellectual functioning of borderline or below average (n = 746 and n = 522). Youth were part of two major validation studies [1979–2017]: MEGA ♪ Combined Samples Studies (N = 3,901 and MEGA ♪ Combined Cross Validation Studies (N = 2,717). Samples were adjudicated and non-adjudicated (males, females, and transgender-female (Trans-MTF) sexually abusive youth, ages 4–19). The measure employed was the ecologically framed MEGA ♪ risk level assessment tool, with statistically weighted cutoff scores (i.e. normative data, calibrated risk levels grounded on given algorithms) according to age and gender. Presented are findings on descriptive characteristics and risk levels of youth in both samples who have low intellectual functioning of borderline or below average. Risk assessment tools for sexually abusive youth need to show sensitivity to developmental issues, gender, and intellectual functioning, with calibrated risk levels according to age and gender.