This study explored whether early elementary school aged children's externalizing problems impede academic functioning and foster negative social experiences such as peer victimization, thereby making these children vulnerable for developing internalizing problems and possibly increasing their externalizing problems. It also explored whether early internalizing problems contributed to an increase in externalizing problems. The study examined 1,558 Canadian children from ages 6 to 8years. Externalizing and internalizing problems, peer victimization, and school achievement were assessed annually. Externalizing problems lead to academic underachievement and experiences of peer victimization. Academic underachievement and peer victimization, in turn, predicted increases in internalizing problems and in externalizing problems. These pathways applied equally to boys and girls. No links from internalizing to externalizing problems were found. © 2012 Society for Research in Child Development, Inc.