I started studying in March with the goal of taking the GMAT April 17. My first GMATPrep practice exam (the first one), I got a 700 (Q40 V46) without studying, so I felt pretty good. I began studying using Princeton Review Crack the GMAT. A few weeks in, I started taking the PR online CAT practice tests. The first test my score dropped to a 650, and then second test after looking over my errors and studying more my score dropped to a 580. I panicked and rescheduled my exam for June 1st.
I came home from school May 20th and started studying for hours a day to prepare. I took another PR practice test and got a 560 and panicked. I was about to cancel my test when I decided to try GMATPrep 2 and see how it went. I ended up scoring a 740, as I wrote before. I kept studying, and a few days later I took GMATPrep 1 and scored a 760. I self-studied using PR's Crack the GMAT and Kaplan 800. Actual GMAT was yesterday and I scored a 730 (Q47 V44).
Hope that helps!