Definition: Internalizing behaviors are actions that direct problematic energy toward the self. In other words, a person who shows internalizing behaviors does things that harm him or her self as opposed to lashing out at others (which are externalizing behaviors). Internalizing behaviors include eating too much or too little, feeling depressed, abusing substances and cutting.
Troubled tweens often demonstrate internalizing behaviors. For instance, internalizing behaviors have been found in victims of bullying, in bullies and in obese tweens. Internalizing behaviors are more likely to go unnoticed and are more "socially acceptable" than externalized behaviors, which directly affect other people.
Related term: Externalizing behaviors
Phares, Vicky. Understanding Abnormal Child Psychology, Second Edition. 2008. Hoboken, NJ: John Wiley & Sons.