It's important to remember to study in layers.
Maths is not about reading it is activation by doing the exercises.
Same goes for science.
Unless you have a super visual memory and can seen the processes in your minds eye as you are reading you will need to do two things,
1, chunk it down. Doing it in segments or better yet
2. Do the experiement, or maths to see it in action.
History,
Who, what, why, whe,n where, and how... mind map each of those question.
Language
PhotoRead, grammar books, vocabulary list, dictionary, exercise books daily. Supplement by activating a few teenage readers, Listening to the language through TV or Radio whenever possible and using the language whenever possible.
Remember too, without a purpose you don't know what you're looking for and don't know when you're done.
Alex