I think the best way to know if students are understanding the material is by quizzing them at the end of a lesson or through their grades in the class. It is almost impossible to teach students everything they could possibly know on one subject, however, making sure they have everything they need to know and are able to apply that knowledge in the future is the best thing you can do for them as a teacher. I think students become engaged with more hands-on activities, however, not every student learns the same so possibly switching up the activities you do every day to teach students a lesson. This way, students are not falling into the same learning pattern. Videos are really helpful when it comes to engaging students, as well as class discussion, and virtual games.