Plickers is a classroom response app that teacher can use very easily without having devices for each student
Plickers lets you poll your class for free, without the need for student devices.
Just give each student a card (a "paper clicker"), and use your iPhone/iPad to scan them to do instant checks-for-understanding, exit tickets, and impromptu polls.
Best of all, your data is automatically saved, student-by-student, at plickers.com