It is probable that Parata's trust in Longstone was seriously eroded by the class size debacle.
And it may be Parata's hope that the secretary's departure will draw a line under what has been education's annus horribilis.
It is a misplaced hope. Longstone's resignation will give oxygen to the Opposition to put their focus back on Parata.
Longstone also has her admirers. She has fronted publicly on almost every controversy and been a straight talker, when the modern practice of chief executives is to hide behind flash press statements written by communications managers.
She touched a chord when she wrote in the foreword of the Annual Report that we in New Zealand "are not entitled to call ourselves world-class while our education system continues to underperform for Maori and Pasifika learners".
The teacher unions savaged her. Parents applauded her guts.
Key has a reshuffle to announce after the election of a Speaker on January 31 to replace Lockwood Smith.
He will spend part of the summer thinking about that reshuffle and whether he has been given a golden opportunity to include education.
Bill English has been a long-time political patron of Hekia Parata. He may help to protect her from the common wisdom that she has been promoted beyond her ability.
Another factor in Parata's favour is that there are very few candidates well placed to shift into the job in mid-term. Steven Joyce has tertiary education but he is totally focused on economic development. Tony Ryall could do it standing on his head but could Key risk losing him from health?
The most suitable candidate is probably Judith Collins, in which case the education sector could come to regret that it wished for Parata's resignation too.
Or Key could do a David Lange and give himself the portfolio.
Key leaves tonight for his holiday home in Hawaii. He will have some big calls to make when he returns.