I'm going active duty from the Guard this coming January. Do you have any recommendations/sources on how to boost my GT score?

So, the AFCT's two most heavily weighted sections are two sections of English and two sections of math. While you want to be able to succeed at the other sections, these two are the most prominent ones in term of the final grade. The rest are just there to measure your potential for various military jobs.

For the math section, I recommend using the Khan Academy to get your skills up. I can't express how amazing this toolset is for anyone struggling with math. I have a keen interest in physics and in order to work on calculus, I turned to this site.

I also used it to raise my own GT score beyond what it was initially and saw approximately a 20 point increase just from putting in roughly a month or two of study through the site.

For the rest of it, there are some people here who have made excellent suggestions. I come from a standpoint of preferring self-study to structure (INTP/introvert), if that's you as well, they sell excellent ASVAB prep books and usually you can find them on a base library nearby, even if they may be a year or so out of date.

The "magic number" to shoot for is 110. That opens the door to warrant and officer, but also opens the door for several MOS's which would normally not be available depending on how low your GT score is.

In any case, good luck.

SPC,
I recommend taking a FAST Class, you can sign up at your local Army education center.

I'm also going Active Duty from the Guard. Just got my signed 368 back on Monday