The research says good feedback has significant impact on student learning. (If you want to check that statement, you do not need to look farther than Marzano's meta-analysis in What Works in Schools.) The research strongly supports gathering effective assessment to drive instruction and giving helpful feedback to students.
Obtaining, analyzing, and acting upon feedback is a critical part of being a classroom teacher or school leader. When I want feedback, I like Survey Monkey. Survey Monkey is free for up to 10 questions with some limitations. If you work at either of my schools, you have access to a school account for Survey Monkey.
Survey Monkey is powerful because you can ask any type of question and obtain feedback in many forms. Some examples include multiple choice, checking all that apply, open-ended responses, and rating scales that are automatically tallied for you. Analysis is easy with the tallying of most common answers and easily sorting or filtering results in a number of ways.
One of the best parts of Survey Monkey is the ability to export to a spreadsheet file such as Excel. As Survey Monkey doesn't specialize in analysis, this feature allows many more uses than the basic summary through an export to a spreadsheet. Organizationally, this tool has tremendous benefits whether it is evaluations, signups, accreditation surveys, exit surveys for staff and students, or just general staff or student feedback. It is a good way to collect data quickly and get a sense where people stand.
In a classroom, this could be used to get feedback from students. I would consider even making a blank survey with numbers 1-5 and choices A-D. I could orally check students understanding of the previous day's material or check for understanding at the end of a lesson by reading a few questions aloud. It's not designed for summative feedback but could serve as a tool to ascertain where students are in their learning, and allowing me to adjust the lesson(s) appropriately. By leaving the questions blank, I could just use it any day by orally giving questions and then reset it for use again. It could be used as part of a larger plan or I could spontaneously get students feedback in a 1:1 laptop setting. Without 1:1 laptops, I could have students do a short quiz for homework (no grade, but just a check) with multiple choice or open-ended answers.
It is worth noting that I would not use it for summative assessments or any significant grading due to the potential for cheating by students. However, it is very valuable in the formative sense for just seeing where students are.
I know some colleagues that also use Google Forms as part of the Google Docs/Spreadsheets package. This can work as well but I find that Survey Monkey is more powerful and in many ways easier to use depending on your purpose. Others use quizzes or surveys on Moodle and Quia is also used by some. Perhaps this will help you find quick ways to get some feedback and see how your students are doing in their learning.