* Extracurricular activities are activities that are *separate* from the school's academic curriculum. They are voluntary and often take place outside of regular school hours. Examples include sports teams, drama club, debate club, student government, chess club, volunteering, and community service projects. They enrich a student's life but aren't directly related to their academic studies.
* Cocurricular activities are activities that *complement* or *enhance* the school's academic curriculum. They are often integrated into the school day or school schedule and may be directly related to a subject being studied. Examples might include a field trip related to a history lesson, a science fair, a class play, a school newspaper, or a research project done outside of regular class time but directly applying classroom knowledge. They strengthen and extend learning experiences connected to the curriculum.
In short: Extracurricular activities are *additional* to the curriculum, while co-curricular activities are *connected* to the curriculum. The lines can sometimes be blurry, but the key distinction is the degree of connection to the academic program.