The use of formative assessment in the classroom provides insight into what students "get" and what they need for instruction/practice with. As opposed to a summative assessment which assess students ability to demonstrate content knowledge or a skill, a formative assessment assesses students progress towards content knowledge or a skill. Think of the summative as an autopsy and the formative as your checkup to see how you are doing.
Too often the effective use of formative assessment strategies is overlooked in the classroom. A typical lesson plan template as a section for assessment. What is typically written there is the same statements that have been copied and pasted from previous lessons. "Teacher observation, questioning of students..etc.." What is usually lacking is a more specific assessment strategy that will be used to adjust instruction.
Technology has provided a tool to assess entire groups of students in order to quickly and efficiently receive group and individual feedback. The use of student response systems such as Smart Response allows teachers to poll a class and immediately view a consensus or access a site to view individual responses. Free web-based services like Poll Everywhere or various Iphone/Ipad apps provide the same experience using your phones.
Exit cards are another great way to check for understanding. How about having students write on sticky notes a question they have about the lesson, a summary of what they learned or a sample math problem from the homework. Maybe have them keep their responses to under 140 characters and post them on your Twitter board as they leave class. This may be an actual Tweet or a sticky note posted on a small paper board hung on your wall.
Google Forms can be used to create a quick quiz or assessment. The results are tallied in a spreadsheet and can be sorted or represented in graphic form with the click of a button.
There are hundreds of great ways to use formative assessment strategies in your classrooms. I encourage teachers to explore the use of active, formative assessment to check for student understanding. Transitioning from "who does not understand?" or "Who needs help?" to a more individualized and personalized method of checking for understanding will have a significant impact on student learning in your classes.