In high school and college when I was assigned a research paper I had the benefit of having access, through my school's library, to a variety of databases filled with scholarly articles. In college these databases could be accessed online through the library's website, but in high school they were only accessible on the library's computer (that was 10+ years ago so it may be different now). I am sure both my high school and college had to pay for costly subscriptions to these databases of information.
If your school lacks these resources, if you can't get into your school's library due to scheduling conflicts (ours totally shuts down during AP testing), or you want students to be able to access high-quality sources at home, Google Scholar is an excellent free online resource.
Just as you would when using the Google search engine, entering search terms will display a list of related results. Under each result is listed the number of times the source has been cited. Also under the result are the options of "related articles," "cite," and "save."
Before having students begin research for an assigned research paper, you may want to familiarize them with this site and discuss how to research. Ask them how the "related articles" feature can help them with their research. Have students examine sources that have been cited frequently and infrequently and the reasons why they think that is (older versus newer publication, more or less credible, etc.). The "cite" feature formats the citation in MLA, APA, and Chicago. Discuss the different purposes and usages of the different styles. The "save" option allows students to save the article for later reference.
You can also have students create alerts for topics, which sends the search results to them as new publications are released. This would be especially helpful if students are doing a long-term research paper or researching a very current hot topic.
As students are working, they can return to "my library" to see all of their saved sources or "create alert" to add or edit alerts.
These features are also located on the Google Scholar homepage.
Two other important features are the "metrics" and "advanced search."
Under "metrics," the top publications are listed as well as other language options. Regardless of their research topic, have students look at these top publications and identify qualities of high-quality sources. ESL students may benefit from the other language options.
Have students play around with the advanced search to see how limiting or broadening their search terms changes their results.
You can see how easy Google Scholar is to use. I love that its simple site name is easy to remember, and best of all it is free and accessible anywhere. Hopefully Google Scholar will be a tool you can use with your students next year for writing research papers or just practicing research skills.