In an affidavit Clague said the couple had argued in the driveway of their home and Ms Jackman became "hysterical". They had fallen backwards when he stumbled after putting his hands on her shoulders, trying to calm her.
Ms Jackman said she was pushed.
The next day, Ms Jackman went to a doctor and said she had fallen down stairs but did not mention the confrontation with her husband.
Doctors found she had suffered severe bruising and an X-ray confirmed she had injured her tailbone.
The pair separated in April 2012 and four months later Ms Jackman filed a relationship property claim with the Family Court.
Clague responded with documents opposing that claim and days later his ex-wife made a police complaint about the 2010 incident.
Because the alleged assault had happened more than two months earlier, police could only issue him with an official warning and the case simmered until March 2014 when Ms Jackman filed a private prosecution.
Clague had quit his $385,000-a-year job as Kristin School executive principal a couple of months beforehand and moved overseas earlier this month.
His lawyer Mike Lloyd said the case was an abuse of process and "continuation would be unfair and unconscionable".
In his submissions in support of the application, he said Jackman brought the charge "in bad faith" and the delays in the private prosecution making its way before the court were prejudicial to his client.
But Judge Sinclair said the points made did not meet the "very high threshold" to have the charge dismissed.
Despite a possible trial hanging over their new head teacher, Britain's The Telegraph newspaper reported that the school's governing body had vowed to stand by Clague.
The school's chairman of governors, Stewart Towe, said: "Bromsgrove School governors are wholly satisfied with the integrity of Peter Clague and followed due diligence in the appointment process.
"The governors are very much looking forward to welcoming the new headmaster and working with him to further develop the school's success."
Bromsgrove boasts more than 1500 pupils aged 2 to 18. Fees per term range from $9400 for a day student to $17,700 for a boarder.
Clague's case will be back before the court next month when a trial date will likely be set.