Locking Lessons During Assessments

Hello! 

After working on several courses, I am just seeing that users have access to the lessons as they are taking the assessment. A user can stop at a question they do not know, click into the lessons, then click back to the assessment and be right back at the question they were on. If they have access to the course materials as they are taking the assessment, it is like taking an open book test. This may not be an acceptable practice for some compliance based assignments. 

Can you lock the lessons while an assessment is being taken? Or, is there a setting where the assessment restarts if the user clicks into a lesson?