I'm PCSing from Korea with a DEROS of March 12, school date of April 25, and report date to Fort Lewis of July 10. How can I make it work?

Your DEROS is irrelevant. It is just the date your not allowed to leave prior to. Once you put in your leave form your DEROS will be adjusted to whenever you're flying away.

Any update on this SGT?

If I'm not mistaken, I think I saw retention or submit 4187 to readjust my deros date. Speak with those guys or S1 to see how you can get those few days adjusted to close that gap.....I see what you are trying to do. PCS Korea enroute to school, then 30 days leave and report to duty station....... That would be a huge stressor on you to move family before school. You don't want to go to school and not be focused because you are worried if you're family back in a new place is doing ok......... I would talk to retention or S1 asap to see if they can go in system to change deros and take SFC advice and verify with S1 about the DA31.