Many students don't know how to study. Study skills are not regularly taught so students do what they think is studying -- reading over their notes, highlighting the text, rereading... Research shows that these are not effective strategies. In Re-Reading is Inefficient, (www.vox.com/2014/6/24/5824192/study-smarter-learn-better-8-tips-from-memory-researchers) Stromberg provides key points from Make It Stick: The Science of Successful Learning by Mark A. McDaniel and Peter C Brown.
There are many strategies for studying that can improve learning for students. For example, there are pre-reading activities which can go a long way toward helping students comprehend texts. A couple of other simple but effective tools include how to take better notes and how to organize information to enhance retention. The bottom line is that learning how to learn can make a significant difference for academic success.