Set the expectation in the classroom that you want to know when someone doesn't understand part of a lesson. Support this with a positive environment, which encourages questions and knowledge checking. Tell students how they should notify you when they don't understand something, such as by raising a hand or by giving a thumbs up or thumbs down. Let students know it is okay if they do not understand something, and it is best to let you know about it.
Actively observe students during the classroom instruction. If a student seems off task or doesn't seem to be paying attention, it is important to determine if they are behaving this way because they already know the material, or because they do not understand the material.
Create ways for students to let you know they are having trouble understanding the material that allows the student to notify you privately. While some students are quick to raise their hands, others may be shy no matter how much you encourage them to speak out. Provide a drop box where students can drop a note if they are having trouble with something. Check students' comprehension of a lesson following instruction by requiring them to write down what they understood or didn't understand and having them turn it in.
Ask students questions about the materials. Avoid asking basic true/false or one-answer questions. Ask students questions that are open-ended and require critical thinking skills instead. Avoid calling on the same students frequently, or only calling on those who raise their hand. Make answering questions fun by giving students access to the marker board, or playing a simple game to determine who can answer the question.
Assess understanding regularly; do not wait until the end of a section. Giving quick quizzes of the previous lesson can be helpful to assess understanding, while reinforcing learning for students who did understand the material.
Plan time for students to learn cooperatively and ask each other questions. Establish a classroom community so all students demonstrate citizenship and feel a sense of duty for the overall class's learning. This can be accomplished by group activities, partnerships and whole class activities. Some students might be more likely to check their understanding with their peers.
Display a positive and open attitude at all times. If students see you frustrated with their challenge in understanding something, or see you get upset with a student who does not understand the material, they are likely to be hesitant to let you know when they don't understand something. Always show your students that you want them to understand and believe that if they do not understand, that you are responsible for trying to teach them using another way.