Plagiarism interferes with a student's ability to learn. A student who copies and pastes information into his essay is unlikely to remember or understand the subject he is writing on because he hasn't spent the necessary time thinking about his topic or exerted the mental effort needed to put the ideas into his own words. Copying information from another source also means the student won't get to practice -- and improve -- his writing skills. When he goes on to a more difficult class in middle school, high school or college, he will lack the writing and research skills needed to write more advanced essays.
A student who is caught plagiarizing usually receives a failing grade on the plagiarized assignment. In some classes -- typically those where students only receive a few grades -- failing a single assignment may mean she will end up with a D or F in the class because she can't earn enough points for a passing grade. Other times, an instructor may automatically give a student who plagiarizes a reduced or failing grade in the class. Instructors may be more likely to impose harsher grading penalties if the student appears to have deliberately -- rather than accidentally -- plagiarized.
A student who plagiarizes may face sanctions from his school beyond simply failing an assignment or class. He may be reported to the Judicial Affairs office and face an investigation. Some schools give the student an official written warning or take away his right to use various school facilities. Penn State gives some plagiarizing students an XF grade, which means "the student failed a class specifically because of Academic Dishonesty." At Strayer University, some students who plagiarize must take an online plagiarism course and pass a quiz on plagiarism.
In cases of severe plagiarism, a student may lose her privilege to attend school. She may be placed on probation with a warning that her position at the school is in danger. She may be placed on immediate interim suspension, which bans her from attending classes or coming onto school property. She may be suspended for a period of time, such as through the end of the semester. In the most extreme cases, she may be permanently expelled from the school or have her degree revoked.