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.........that if one is applying to the same schools law program as he/she went to undergrad/grad school, they will have a slight but measurable advantage? Or, is this nonsense?

Maybe- but it's still going to be mostly a numbers game. A few schools (GULC, Mich) have a special application program for their undergrads that can get them out of taking the LSAT.

Can't be evaluated. Depends on the school. The best known case is GPAs from Harvard undergrad being .05-.1 below those of other undergrad GPAs at HLS. Besides that, no idea. As to measurable, hell no. I would say .1 GPA compared to getting into Harvard is more like a really cruel joke.

Maybe in the sense that you picked them before so you are more likely to pick them again, and so you may be slightly more likely to boost their yield and less likely to get yield protected. You'd also probably be able to write a strong "Why X" if necessary. Not anything big though, definitely approach it as if you weren't getting any advantage.