Students tend to be more engaged in a class when they feel like they are an active part of the learning process instead of just a bystander.  One thing that I always enjoyed was allowing the students to help guide where we would go next in class or how we would go learning about our next topic.  Setting up a Google Form to get feedback from students to allow them to help be part of the decision process can really have an impact on their engagement.  Engagement should be an integral part of any learning environment.

Before you start that next unit, set up a Google Form with a couple of quick questions to allow the students to vote or give feedback related to either the focus of the learning or how the learning happens.  I think many would be amazed at the increased engagement when the students have a voice in the learning process.