Will I be able to reverse the effects of chronic sleep deprivation (by getting more sleep)?

Well, I'm only 15, but for at least 2 years (so maybe not chronic sleep deprivation- but at least habitual?) I have really missed out on sleep. I've regularly gotten 4-6 hours of sleep on the weekdays, on some days 2-3. I sleep for really long on the weekend and then get only 1 or 2 hours before Monday. Since teenagers are supposed to have almost 9 hours of sleep nightly, I'm afraid I've really messed myself up. I used to be a straight A student, and I still do ok in most of my cles (although I have only 4 and 3 are easy), but in math I've just gone straight downhill since the sleep deprivation started. I make the stupidest mistakes and can never follow what the teacher is saying at all and just cannot concentrate AT ALL. So anyway, I was just wondering that if I changed my sleep habits now, would I be able to avoid any permanent, say, loss of thinking, memory, or attention? Just wondering :( Also, advice on breaking the habit?