Somewhere in 2018, I was appointed as a teaching assistant within our research group, evaluating and reviewing students’ papers and assignments, including checking their works for plagiarism. I had the opportunity to use Turnitin for this task, one of the popular plagiarism prevention services in the academic field. Since I have been several times assisting some lecturers who found difficulties in checking their student’s works, my interaction with this platform until quite recently can be said as fairly often.
Along with the frequent usage, I noticed a few things in particular about this software and how academic staff from my institution interact with it. The following note could be a good insight if you’ve never used this software before.
Turnitin is not a free software
This is quite obvious. Yet it is also not a service we can personally purchase for personal use. The company only makes its software available to schools, universities, and other institutions (mostly academic). The licensed school or university can then use Turnitin by assigning Instructors (in this case, teachers or lecturers) to give access to students to check their papers.
Enrolling students in a class
What the instructors should do to let students use the service is by letting them enroll in a class. But before that, these students need a student account at Turnitin (read the details here). The other things they need are the Class ID and the Class Enrollment Key that should be shared by the instructors.
If you are an instructor, you can find the Class ID next to the title of the class, as depicted in Figure 1 below (data redacted). Take note that you shouldn’t share the Class ID of the master class. Instead, share the ID of the normal section derived from the master class. This is because you can only find the Class Enrollment Key from the class sections.
The Class Enrollment Key is something the instructor should make on the settings of the class sections. The option appears after the assignment settings of the teaching assistant (TA). See Figure 2 below.

Sharing both Class ID and Class Enrollment Key will allow students to access the class and submit their assignments for plagiarism check.
The problem of ‘immortal’ classes
It appears that, based on my observations and from a help page published by Turnitin, the number of enrolled students relates to the fees an institution pays for the service, i.e., the purchased license valid up to a certain number of students. This is confirmed in a statement by Turnitin, where students in ‘expired’ classes do not count against the institution’s student limit.
However, the problem arises when instructors do not expire outdated classes (as some of them probably forgot), making students from a previous term still get counted towards the student limit. That means for a certain share, the institution pays for unusable services.
I have a presumption that there have been multiple cases where an institution lost quite a good amount of money over such circumstances, forcing them to regularly remind their instructors to regularly check the end date of their classes.
Some settings are being overlooked
Another thing I noticed is that some settings in the Assignment section of a class are often overlooked by the instructors. This is particularly true for the repository settings where papers would be submitted to. However, since the said setting is available only when the instructors check the “Optional Settings” of a paper assignment (Figure 3), this matter is sometimes being ‘skipped’ by the academic staff.

The Optional settings contain some critical setups that determine how the service would behave in checking the student submissions against the repositories. These include whether bibliographic and quoted materials should be excluded from the Similarity Index or not. Also, whether small sources will be counted or excluded towards the final similarity score (Figure 4).

The most important setting, in my version, is whether or not the submitted paper should be stored in the repository (Figure 5). I happened to find more than one cases where a submission resulted in a 100% similarity when actually the percentage should be significantly lower. The issue is that those cases occurred to doctoral thesis manuscripts prior to their publications. I can’t be certain if these manuscripts were deliberately submitted to the repository or not, as the second time a student would like to check their ‘updated’ manuscript, which usually has only slight changes, the system will check it against their own former drafts. This, of course, may lead to a significant share of similarities somewhere between 90 – 100%.
In my opinion, despite the easy solution where instructors/students can simply rule out the main source of the problem (the reference to the former drafts), there should be a sense of secrecy as such manuscripts contain a lot of sensitive research data. If research funding takes place, then it wouldn’t be wise to store such a manuscript in the repository, no matter how reliable the system or the admin is. Submitting the document to the repository is not the same as publishing it, where you can claim the authorship of the thesis.
The last area where instructors check the least is the ”Search options” feature (Figure 6). By default, all three sources of student paper repository (internal), current and archived internet, as well as periodicals, journals, & publications should be included for an extensive search. However, one or two sources can be excluded from the search options in practice. For example, if an instructor feels like his/her student paper repository has been saturated with similar short essays (submitted as an assignment every semester), he/she can rule it out by unchecking the box and proceed with the plagiarism check with only the remaining two sources.

There are other peculiar habits I found from different Turnitin users in my institution, from simply favoring the Quick Submit feature (without bothering to set up even a single class) to steering clear of using the student enrollment feature, but the above matters attract me the most. But after all, they all return to the individual style of the instructors.