Study Habits: How can I retain information from textbooks with a lot of reading in order to prepare for an "A" performance on a quiz/test

You forget the content because you're not successfully interrupting the process of forgetting. Test yourself often and without your source material. When reading a text, instead of taking notes by listing out facts from the source material, take notes in question form when you come across a fact you'll likely need to recall later. For instance, when learning about set theory, instead of copying the definition of a set from your book, write 'What is the definition of a set?'. Later, when reading through your notes, you should try to recall the answers without source material. If you can't recall something, then you're free to return to the book and look over the information again. The important thing is that you expend effort to remember something; learning without that effortful recall will not be durable. Perform free recall. Once you've finished reading a section of material, or every 10 minutes - whichever is sooner - close the book and attempt to summarize what you've just read. Ask yourself 'What were the important facts that I just learned?' 'How does what I just learned fit into the structure of my other knowledge?' 'How would I explain what I just learned in my own words?' Create mnemonics for information that is organized as a list, or that is crucial to remember. Mnemonics can include acronyms, using the Major system for numbers, creating songs that link lists of items together (this is how you learn the alphabet if you're in the US). Solve problems before you know the answers. Read your textbook backwards from each chapter. Attempt to answer questions without having gone through the source material. Connect what you're learning to what you already know. Ask yourself questions about how the material is similar to material you already know. If you know about cars and hydraulics, then how is the human body similar? Think of real-world examples that come close to modeling the natural phenomenon that you're studying. Don't cram. Learning that occurs within a short period of time isn't durable. Use spaced repetition. Read online for programs that help you put information into a spaced repetition format. http://ankihttp//ankisrs.net/ - Anki is an excellent resource. Reflect on the practice of your skills and ask yourself 'What could have gone better?' 'What went well?'. From your reflection, generate some plans for behaviors to change or things to experiment on. Teach others the knowledge that you're learning. Trying to teach another person highlights all of the gaps in your understanding. If you don't have anyone to teach, step up to a whiteboard in an empty classroom and run through the subject yourself. This is also known as the Feynman Technique. All of these techniques are discussed in more detail in http://www.amazon.com/Make-Stick-Science-Successful-Learning/dp/0674729013/ref=sr_1_1?ie=UTF8&qid=1432146154&sr=8-1&keywords=make+it+stick

Generally there are two ways of going about retaining information: - learning concepts and spaced repetition with various ways of testing your memory - memory techniques (such as mnemonics, 'memory palaces' etc.). Both require active learning (reading texts is usually not enough) and recall practices. Let me repeat it again: reading texts is not enough to retain information. Practice on old quizzes in exam-like situation (e.g. by timing yourself, sitting at a table etc). here is a few more tips on reading textbooks effectively http://www.slideshare.net/ShapeShiftersClub/how-to-read-a-textbook

I was recently contact by a student at Yale asking to write for a website called http://IntelligentStudying.com (I ran quite a successful private tutoring business in college based on my study methods, must still have some kind of reputation). Though the article I wrote for them was about understanding math and quantitative concepts, I did check out the rest of the site and there is definitely some quality stuff on there about how to approach studying in more effective ways. As I recall there were articles about better retention and learning, smarter ways to read textbooks, and how to take tests well. It's great that you're asking the question, I personally am a big fan of smarter approaches to studying and feel that unique methods were what got me through Yale with a high GPA.My biggest piece of advice is to read up on various approaches and tactics, find some that seem interesting to you, and then commit to learning a great deal about this selection and implementing them into your habits. Pick up one mindset or approach at a time, but really pick it up well. Just one that you are serious about will have a huge impact on your success, but having lots that you half-ass will be less effective.

The best way to retain information is to write it, copy it, re-write it, summarise it (in writing), and so on. Merely reading isn't enough for most people. I'm assuming that this particular subject is heavy on facts and figures? Otherwise learning to regurgitate information might not be the best learning strategy.

It depends a little on how you learn, but if you want to retain what you read, you have to act on it.  If you are a mechanical/kinetic mind, write a summary of each section. If you are auditory, read relevant sections out loud and listen to yourself. Actually memorizing parts will help as well.  If there are problems or exercises, do them.  That is most important.  Doing the subject will always trump reading about it. Another sure way is to explain it to someone else so that they understand the concept.

You might try practising the SQ3R study method. For details, please see my answer here:  

Flash cards are your best friend. Make sure you write the information you're trying to learn, for me I've found it to be most effective by actually writing it- not typing it. Review the written information as much as possible, maybe even write it down again. Never cram a lot of information you wish to retain at the same time.

You might have found the answer by now, Paul, but I'd just like to remind you that  'really wanting to do well in school' might be something you want right now, but after some time, it won't matter much. So do not overburden or stress yourself. Even if you're not able to achieve what you want in school, that is not the end of the world. Life goes on!