One of the things that looks like a clue to me is that this the lead engineer of close.io. Browsing through their site, it looks like they do "telecom in an API"; it reminds me of Twilio and OneBox.
So, here's a thought. Let's say the Engineer has access to the SMS logs (NSA-style) for Justin's phone. (Maybe his phone goes through their system. But even if not, maybe it's company-provided, so there's an admin interface provided by the telecom that lists this information.)
Justin probably doesn't regularly text people in Texas, since the team is based out of Palo Alto. So look through his logs for a number in a Texas area code (http://en.wikipedia.org/wiki/List_of_Texas_area_codes) that he's been texting more often than usual.
That gets you the girl's phone number; probably a cell phone. Now, you need to go from the cell phone number to a last name. Reverse Phone Lookup probably won't work for this, although it's certainly worth a first try. More likely candidates: looking through the users table at close.io for a matching phone number, or doing a google search for the phone number. Or, try calling in the middle of the night and seeing what the voicemail says. Any of these approaches might work.
Once you've got a last name, grab a copy of the white pages. Most public schools publish their district boundaries, so go grab a copy of that. Look through all entries that match the last name, and see how many of them fall within (or close to, in the case politics made the boundary change) the district boundary. You probably will get a handful (maybe three or four). If you only get one, bingo!
If you get more than one, I'd call the cell phone to see if I can get a first name somehow. Then, I'd go through the landlines in the White Pages and call them one at a time, "Hello, may I speak to X? Sorry, wrong number." until one matches.
