After quitting Westlake, he immediately started full-time work, before travelling the world and then enrolling at university at age 22. He gained a law degree, and then a masters degree in history.
He worked at top law firm Chapman Tripp before moving to London, where has worked at international law firms ever since.
Crawford's speech was secretly recorded by a Fraser High student, who posted it online.
It has been reported that students will stage a protest this week by collectively wagging for one period.
Crawford did not respond to a request for comment, but Board of Trustees chairman Jeff Green said the school had received a "great deal of positive feedback" on her speech.
He said the board was very supportive of its principal "for being strong enough to have challenging conversations with our students".
"Everyone on the board of trustees, in the senior leadership team and on the staff at our school wants to equip each one of our students with the best possible education and tools for life.
"We consider that even if just one student reconsiders the path they are taking and takes steps in a more positive direction after this speech then that could have huge impact on their future lives and those of their family and friends and wider community."