Plagiarism negatively affects the whole classroom. If caught, the plagiarizing student's grade, and possibly their academic career, can be severely affected. If the plagiarism is not caught, other classmates may feel like their hard work and honesty are meaningless, and be tempted to cheat themselves.
One technique I have found to be helpful in identifying plagiarism is asking students questions about their writing. If a student can't answer a question such as "what did you mean by this sentence?" or "can you clarify the point of this paragraph?" then most likely it was copied.
To address the "what is the impact" portion of your question...I think one of the huge impacts is the waste of time and resources. If the teacher has to double check student papers (feeding them through check systems) it takes time away that s/he could be spending helping struggling students, challenging students, doing research for class presentations, etc.
As to the question of "how to deal with plagiarism,"...I was recently talking with a professor who said that she spends the first day of every new class teaching the kids what plagiarism is. She models various forms and then hands out sample student work, asking students to identify which are problematic and which are not. All too often, I think students plagiarize without meaning to...they just do not fully understand the appropriate way to cite various texts.
One of the first elements that a teacher needs to address before giving any assignment is what plagiarism is. I present a handout to my students with the various forms of plagiarism on it because in the past we have had students try to argue that they did not know they were plagiarizing.
We read the description together in class, and my students sign that they have read and understood it in its entirety. I then send home a copy which parents are required to sign because in several parent conferences, parents have taken their child's side and argued that something was not an example of plagiarism. This method has helped prevent quite of plagiarism.
I have also required a lot of writing in class as another teacher noted because it is very difficult to plagiarize in a setting like that.
What of the most significant effects that plagiarism has had on education is increasing a teacher's work load. Teachers now have to check all sorts of sources to make sure that students have plagiarized and then have to be willing to deal with numerous principal/parents meetings if they believe that a student has plagiarized.
Plagiarism is a problem that teacher's face in today's classroom. When a student works hard at an assignment they learn that it pays off. They gain self-respect and confidence.
Almost every student either has a computer at home or has access to one on a daily basis. It is very easy to see what others have said about a topic and either copy it or re-word the text. When student's take this route they learn that it's easier to ride on someones shoulders than to work hard on their own. Eventually, this backfires. When student's plagiarize they aren't learning the crucial skills needed to be a productive adult.
Student's need to be taught that plagiarism is wrong. Honesty is always the best policy.
I have my students create research notecards, where they write the quote or statistic in a specific format, need a number of different sources and types of sources, then I go through the notecards and reject the ones that don't meet the criteria.
Then, instead of typing the paper (read: cutting and pasting from some other website), I have them write it in class, in front of me, in pen, during a class period. Then they have to express everything in their own words, with their supporting info. The fact that you look over the notecards ahead of time is the key to preventing plagiarism because you can limit what they put on them.
I never give worksheets as homework - ever. Stduents will cheat off of each other every single time, even the best students. They're almost worthless as learning instruments.
Another difficulty that I see in today's classroom is that students from some other cultures find our documentation requirements alien. Not all cultures document the way we do, and the educator must take the extra time to help the student from another culture learn how to meet the expectations. In some cultures, it is a sign that one is learned to be able to incorporate the ideas of others into one's writing or speech, without attribution. One's audience is expected to understand, which is a sign that the reader or listener is learned, too. This is a kind of cultural "coin" that is common in other cultures. I review the writing of many ELS students, and this is a striking difference that we must take into account. I have included a link that discusses this idea in greater depth.
Plagiarism has become an easy way for students to complete assignments without having to do any real work for them. With the advent of the internet it is easier than ever to plagiarise. Intodays society I believe that the some members of the current generation lack the ethics and morals of the older generation and just don't care or take pride in their work. Plagiarism encourages a lack of motivation and self respect in students. Students who plagiarise will miss out of learning skills which are essential in many careers and become accustomed to being lazy and not using their minds.
As students become more internet savvy and more aware of what is out there online to help them, the impact of plagiarism is much more prevalent and meaningful to the modern classroom. I think that there are some pedagogical steps which can be taken in order to ensure that this is avoided. The first would be to have longer research projects broken into chunks, as opposed to assigning and then collecting a final product. Having more opportunities where instructor is able to check on the student progress would allow a greater organic dialogue to emerge as well as allow the instructor to have a greater feel of the authenticity of production. It might also allow the instructor to develop an advance look at the product to be able to identify where original student thought is present, or to stem or stop the flow of inauthentic student thought. At the same time, being able to assign tasks in a backwards format might be an effective way to stem plagiarism. For instance, usually the works cited list and the generation of the sources is seen as tedious and thus one of the last elements undertaken by the student. If instructors make this one of the first tasks to be done, it might be able to help students authentically use outside sources, credit them, and assist in the development of effective thesis statements and ideas.
Plagiarism became an easy way out for those who are not willing to fully commit or exert their full potential. It also shows that a student who plagiarizes has to depend entirely on someone else's thoughts, opinions, and works, rather than try to think of their own position or their own thought process.
A teacher has to instill values such as no stealing, but they have to make sure that they are working as a team and not on their own. You can tell students don't copy all you want, but if other teachers don't care, then you have a bigger problem.
I would like to add a little to above answers with due respect to the answerers.
There are various reasons which lead the learners to plagiarism: lacking of creativity, over reliance on memorizing, a large class consisting too many students to handle each individual particularly, practice of only intensive or limited readings inside and outside the class etc.
Plagiarism, nonetheless, is a hindrance to a student's own creativeness which resists the student learning to form his or her own opinion. This overshadows the development of the imagination power, the ability to think. Plagiarism is one kind of theft, because, here, you are pilfering other's work and giving it your name. There is no credit in plagiarizing nor it helps the students learn something in the real sense. Students are becoming just copy-cats.
The educators or teachers must deal with plagiarism with great sensitivity in the class. They can take following steps: 1) Can motivate learners to read extensively. 2) Can take open book exams. Thus, students will be encouraged to read the texts first rather being dependent on online guides or critiques. 3) Can give tasks that comprise open-ended questions. 4) Can divide the classroom into groups, and by taking bits and sentences from each group, make a whole paragraph or essay. All students need to write their very own sentences there. 5) Students must be informed in the first class that, quotes must be used if sources are taken from outside directly. The educators should teach them not to use long quotations, instead small phrases or words. It will help in minimizing the fear of the learners regarding quotations. 6) If students use any website, they should give the source as reference. For this purpose, they can be taught about how to write in an M.L.A or an A.P.A style. This will be essential while preparing any long assignment or research paper. 7) The educator can, at first, inform the learners that marks or grades would be deducted for plagiarism, and if any student, still, plagiarize, can be given lower grades than others. This should be done to establish an example.
Thus, handling tactfully, educators can protest against plagiarism, and make the students write their essays or answers on their own.