Re-reading is the most common study method among school and entrance students, and one of the least effective. The reason is straightforward: rereading produces familiarity, and familiarity feels almost exactly like understanding.
A test you can run today
Close the book. On a blank sheet, write down everything you can recall about the topic you just revised. What you cannot write, you do not know — regardless of how comfortable the page felt while you were reading it. Most students find this uncomfortable the first few times, which is precisely the point.
Active recall
Convert every heading in your notes into a question. Read the section once, close it, answer the question from memory in writing, then check. This is measurably harder than rereading. The effort of retrieval is what strengthens the memory; passive review does very little.
Spacing
Revisit a topic after one day, then three days, then a week, then a month. Retrieving something you have partly forgotten builds a far more durable memory than reviewing it while it is still fresh. This is also why cramming produces a result on Monday and nothing by Friday.
The practical version
After every class, spend ten minutes writing what you remember before opening your notebook. Then open it and fill the gaps in a different colour. Those gaps are your revision list. That single habit is worth more than an additional hour of reading.