Insecure attachment to parents has been related to internalizing and externalizing problem behaviors in children and adolescents; yet, a notorious research gap regarding preadolescent attachment still prevails. Preadolescent development and cultural fac-tors might favor the development of insecure attachment to parents, deprive Mexican youth from a paramount protection factor during this time of transition, and favor the development of internalizing and externalizing problem behaviors. This study aims to compare means of insecure attachment to parents and problem behaviors between sex and school grades, locate linear and non-linear effects from anxious and avoidant insecure attachment to parents on internalizing and externalizing problem behaviors, and to test whether attachment to mothers present a stronger association with prob-lem behaviors than attachment to fathers. The sample was comprised of 188 students from a public elementary school in Mexico City (56% girls, age M = 9.9 SD = 0.86) from 4th (34.6%), 5th (30.3%), and 6th (35.1%) school grades. Consistent with previ-ous research, differences in insecure attachment to parents between grades were found. Avoidant attachment to parents was found to be lower for 5th and 6th grades, whereas anxious attachment was higher for both these grades. Anxious attachment to mothers was found to be a direct predictor of internalizing problem behaviors and an indirect predictor of externalizing problem behaviors. Avoidant attachment to fathers presents a non-linear effect on internalizing problem behaviors.