"He was motivated by a desire to do the right thing, and I continue to stand by him," Prentice told listeners to CHED and CHQR Friday.
"He's doing a good job as the minister of education.
"It's not an easy position and he has got a lifetime of experience, which is what we need right now."
Dirks did not have a seat in the legislature when Prentice put him in his cabinet in September.
He then won a seat in a byelection in Calgary-Elbow on Oct. 27, but the narrow victory was not without controversy.
In the days before the vote, Dirks promised to deliver modular classrooms to a school in his riding, bypassing other city schools deemed a higher priority.
The opposition parties complained to ethics commissioner Marguerite Trussler.
In a written decision earlier this month, Trussler called Dirks' actions "blatant political opportunism" but said they didn't break conflict of interest rules because there was no direct financial gain.
However, wrote Trussler, "this issue was not one of general policy or ongoing work.
"It was a specific political issue that he used his office to resolve in his favour.''
The Conflicts of Interest Act, she added, "does not deal with moral integrity.''
On Friday, Prentice said Trussler prefaced her comments by saying she would not have handled it the way Dirks did.
"She said if she had been asked, she would have advised to do it differently and she'd be concerned about the optics," said Prentice. "It was hardly a scathing criticism of what the minister did."
Dirks at the time, said in a statement, "Premier Prentice has made it clear he expects everyone in his government to conduct themselves according to the highest ethical standards, and I fully support him in that goal.
"I appreciate the ethics commissioner's observations about perception and politics and I will be mindful of her comments and suggestions in the future.''
Opposition politicians have said the Dirks affair falls far short of Prentice's promise to restore integrity to government following the scandals under former premier Alison Redford.