Because of their neurobiology and resultant executive functioning challenges, young people with ADHD often struggle to keep a good handle on time. They may not have a natural sense of what time means (what does 15 minutes feel like versus an hour?) or of how much they can realistically accomplish in a given time frame. These young people may lack strategies for managing their time effectively, and they may not have the know-how to make good decisions about which task or activity to work on first in terms of high and low priority. Phone calls to friends may be made before homework is completed. The adolescent may sign up for an overload of after-school activities, thinking that schoolwork can be squeezed in after dinner, when senior-year classes are a top priority that require homework be started directly after school. Time management issues may also result in the young person being chronically late for activities or events, failing to accomplish household chores, not getting sufficient sleep because he or she has to stay up late cramming for exams, or falling behind in schoolwork because of too many extracurricular activities.