Well-intentioned teachers today are on a continual search for ways to increase engagement and comprehension in their classrooms. According to several recent articles, the use of Audience Response Systems (ARS) in the classroom can be one tool for achieving those outcomes. In short, ARSs have been shown to increase student attendance, exam grades, final grades, attention, and engagement. [1, 2, 3] The one major objection to ARSs is that the purchase of clickers and accompanying software can be cost-prohibitive. However, one option for educators that has opened up the ARS world is the free opportunity to use the free ARS options at a website called polleverywhere.com.
How it works
Polleverywhere.com is a website that allows teachers to construct multiple choice and open-ended questions that can be used to "interrupt" a lecture in order to take a quick formative snapshot of how well students are understanding the material. [The author has no conflict of interest - He is not a representative of this company, or an affiliate, etc.] One reason to use this particular ARS is that it is one of the only ones that allow you to construct questions in multiple formats. Therefore, instead of being locked into writing multiple choice questions, as with some ARSs, you can also write questions that allow students to express their thoughts qualitatively. Some options for these open-ended questions are as simple as "One thing I don't quite understand is...." Or, "A topic I'm concerned about is..." Or, on a more engaging level, "An example of this topic in real life is..."
When your questions are presented to students, it is through a web-based browser that is projected in the front of the class. After the question is presented, students are prompted to respond to it by texting their answer to a five-digit code that is provided. If available, students without phones can also respond on laptops or desktops. Instructors then have the opportunity to see how many people answered correctly (for MC items), or whether there are any themes in students' answers (for open-ended items). The results of the data analyses that are provided can then be used for further discussion, lecture clarification or toying around with new applications.
Why you should consider using it with your students
There are seven major outcomes that some research suggests can be attained by instructors who use polleverywhere.com: [1, 2, 3]
1) In a typical lecture, when an instructor asks a question, only a small handful of students will volunteer a response. The remaining students are either embarrassed to answer ("What if I'm wrong?"), don't know the answer, or are not paying attention. The teacher has no idea what is brewing in the minds of the students. The anonymity of the responses on polleverywhere.com encourages 100% engagement with your questions, which naturally increases the number of students who are thinking about the material. This is especially great for large classes, where students can easily blend into the walls, and neglect opportunities to reflect on course content.
2) Students whose teachers use the site report that they are more active and engaged. This can be for many reasons. First, there's no risk in thinking about and attempting to answer a question, because your answers are anonymous. Second, the questions can break up the monotony of a lecture into smaller chunks. Some studies  suggest that most people can only focus on a speech for a maximum of 10 to 15 minutes before the mind wanders. If the lecture is broken into 10-minute chunks, followed by a question or two, the change can bring students back to attention.
3) There is increased motivation to try to understand the material. The students in the class who want to do well will be motivated to grapple with the question and attempt a correct answer, in order to get feedback about where they stand. When students are prompted to answer questions in pairs or small groups, some research shows that the conversations they have are truly on-topic and taking the task seriously. 
4) The questions help students clarify their thinking. They get positive or negative feedback about what they are learning, which can give them information about what to focus on when they are studying. This idea is very Piagetian/constructivist , in that errors are powerful sources of information that incentivize people to correct those errors. As one student put it, "The questions are either a confidence builder or a wake-up call."
5) At the college level, there is a motive for increased attendance, because students will get more information and material than what will be found in the book. This includes not only the questions and answers (which may be models for how exam questions will be written) but also the discussion that the instructor facilitates, as s/he reflects on the answers provided by students.
6) Students can use their phones and computers in class! Their precious technology can be seen as "learning enablers, not distractions." Compared to many classroom environments, where technology is prohibited, just the very act of using devices with teacher approval can be exciting, and bring students into the activity.
7) The use of the questions can do a lot for the instructor. First, it requires the instructor to prepare the questions, which can center attention on the material and provide insights about how to teach the material in a better way. Second, it gives the instructor the opportunity to adjust the pace of the class, conversant with the relative level of understanding of the material. Third, the creativity that is required, in order to respond to the results, create a discussion about why the results turned out the way that they did, and think up new examples and applications to make the material more understandable, can increase the instructor's enjoyment level, which may have spillover effects on the students.
The use of ARSs is not a panacea for all that ails you. Answers to questions on a phone are not the same thing as answering deeper questions on an exam. Therefore, in order to keep students from walking away from a class with a false sense of mastery, it is important for teachers to use the responses to well-constructed ARS questions as a platform for taking the classroom conversation deeper. You can ask a question or two, and then ask the students to help you interpret the class responses. Talking out loud with them about what the data say in the aggregate can be a powerful exercise in metacognition.
When used in this way, polleverywhere.com can be a very engaging way to check in with your students, break up your teaching into smaller chunks, and provide them with some feedback about how well they are understanding the material.
 Kappers, W. M., & Cutler, S. L. (2015). Poll Everywhere! Even in the Classroom: An Investigation into the Impact of Using PollEverwhere in a Large-Lecture Classroom. Computers in Education Journal, 6(20), 21.
 Barth-Cohen, L. A., Smith, M. K., Capps, D. K., Lewin, J. D., Shemwell, J. T., & Stetzer, M. R. (2016). What are middle school students talking about during clicker questions? Characterizing small-group conversations mediated by classroom response systems. Journal of Science Education and Technology, 25(1), 50-61.
 Meguid, E. A., & Collins, M. (2017). Students’ perceptions of lecturing approaches: traditional versus interactive teaching. Advances in medical education and practice, 8, 229.
 Benjamin Jr, L. T. (2002). Lecturing. The teaching of psychology: Essays in honor of Wilbert J. McKeachie and Charles L. Brewer, 57-67.
 Piaget, J., & Inhelder, B. (2008). The psychology of the child. Basic books.