If you study hard but score low, the problem is almost always how you study, not how much, common causes are passive reading, no self-testing, ignoring past papers, and weak exam technique. The good news: fixing your method, not adding more hours, is what turns effort into marks.
You may be studying passively. Re-reading and highlighting feel productive but build weak memory. If you cannot recall a topic without looking, you have not really learned it. Switch to active recall, test yourself instead of re-reading.
You may not be practising the right way. Reading solutions is not the same as solving problems yourself. For maths and science especially, you must practise actively; understanding the steps when someone explains them does not mean you can reproduce them under pressure.
You may be ignoring past papers and the exam pattern. If you study everything equally and never solve previous papers, you may be over-preparing low-weight topics and under-preparing what is actually asked. Past papers tell you where to focus.
Your exam technique may be costing marks. Running out of time, poor presentation, misreading questions, and silly mistakes can sink scores even when your knowledge is fine. How you write the exam matters as much as what you know.
Example: A Class 12 student in Bhopal studied for hours but only re-read notes. When she switched to self-testing, solving past papers, and timed practice, her marks jumped, with no increase in study hours.
One practical tip: For one week, replace re-reading with self-testing, after studying anything, close the book and write what you remember. This single change is usually what finally turns hard work into higher marks.