I took the OAR yesterday, scored a 52 on my second try.
The second time I studied the Barron's book and the OAR Study Guide book, both can be found on Amazon. I studied some gouge found on this thread, particularly the Marine Aviation Guide, and the OAR Math Study Guide. I did the math and mechanics sections in the Barron's and OAR Study Guide until I got the answers cold. Then I hit the gouge. Anything that I could not understand I went to Khan Academy.
I am a stay-at-home dad, with a part-time job. I studied about 4-6hrs a week for 3 months.
Math, a little bit of geometry, mainly sequences, and algebra.
Reading, dense Navy HR and science.
Mechanics, just the basics.