Yes it is possible. I am a high school senior and I took the ACT last year without any prep. I scored a 24. I then decided to pay for the $40 course that college board offers on their website. After roughly 20 hours of studying with that course, I took the ACT again and scored a 30. I then took the SAT after another 15 hours of study and scored a 1430, the equivalent to a 32.
If you study a little bit, you will see an increase in your score. If you study a lot, a 34 is possible.