He said he had nothing to hide about his relationship with the Nottingham-based agency, despite an article hinting at close relations between ELS and the Colleges' Employers' Forum, the AOC's predecessor.
Private Eye said Mr Ward, who was the CEF chief executive, had been flown to Boston by ELS to speak at a conference.
And it said an employee of ELS had been present when Mr Ward met representatives of rival agency Nord Anglia.
But Mr Ward told The TES his trip to Boston was recorded in the CEF's register of interests and had been cleared with its chairman.
And he insisted that the meeting with Nord Anglia had included a ELS employee to allow both agencies to bid for work.
He said: "It's no secret that I have promoted the concept of agencies from the early days as one way to create a flexible workforce.
"I supported ELS on the grounds that they were the only company to meet the service standards we set down for any and all companies to agree to."