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I have a huge gap in my two scores. I made a 156 on my first attempt, and my June score was a 167. My GPA is a 3.75, and my dream school is UVA. I know that 167 is on the lower side of what they accept, so I was thinking about applying ED to boost my chances. Should I write an addendum explaining why the 167 is more indicative of my abilities, or should I retake in October to both bring my LSAT average up and prove that I am capable of scoring that high. I feel confident that I could score in the low to mid-170's with a little bit of studying and a lot of PTs.
The addendum would address the fact that I was going to school full time and working graveyard shifts at night, which had me on a reversed sleeping schedule.
Thanks in advance for any responses. You only get one shot with ED, and I'm worried they'll see the 156 and immediately reject my application.

You will be able to retake and ED most places if you have your app together before the Oct test. It's the best of both worlds. And you'll probably want an addendum, too.

Thanks Eugenie, you've been very helpful.
I was planning on having my app ready, and sending it out to some T30 schools on day 1. Should I wait on my new score before I send my app to T14 schools like UVA?

Those numbers are not enough for UVA, even ED. You need to have at least a 3.85 or a 170. Either retake again or aim for the bottom of the T14 (Cornell and GULC) and the T25