I am a junior in high school who wants to achieve a score of 30 or higher on the ACT. I took the exam for the first time last school year, and received a 18. I barely prepared for it, I stressed out the night prior, and I was nervous during the test. However, this is a new year, and I have more material to prepare for the exam with.
I am using:
Sylvan ACT prep- $1,290 dollar course. It starts 2/7/16
Kaplan ACT Prep Book
The Real ACT prep guide-2016-2017
ACT Online Prep- bought from the ACT.
Assuming I use all of these, is it possible for me to raise my score 12 points?
The answer is: yes.
The means, however, will be brutal. If your score doesn’t get as high as you would like it after all of those resources (1.3K$!), don’t throw more money at the ACT and hope it’ll get higher. Nail down your mistakes and ruthlessly go after them.
You’ll get it if you really want it. Write down your motivations for getting a high ACT score: what colleges you want to get into, what you want to be doing in 5 years, 10 years. Look at that list whenever you feel like nothing you’re doing is working.
Good luck.
Edit: I don’t know if this applies to you, but: DON’T drink coffee before the test. I learned that the hard way. You don’t need your heart rate and anxiety level to be any higher due to caffeine.
Anything is possible. It depends on what the factors were in your getting an 18 last year. If it was exposure to content, you should improve and if it was lack of time management you will improve. While I am sure you will improve, if you are not a good test taker (nerves, stamina, concentration) that may still cause issues. Take a practice test under real test conditions and see how much you have improved. That should be your new starting point. I think it’s a bit of overkill on the prep materials but whatever works for you. 
This is going to sound harsh. But your chances of raising your score from 18 to 30 are extremely thin. 18 isn’t even median (it’s 43rd percentile). And your goal is to be 95th percentile. Realistically, unless you simply skipped half the test on a whim for your “before” test, you’re not going to raise it 12 points.
Have you tried the SAT instead? Some people are better at one vs the other.