When a special education teacher at M.S. 302 in the South Bronx found out in late 2009 that, like so many other Americans at the time, she was at risk of losing her house to foreclosure, she went to her assistant principal for help.

The assistant principal, Larry Thornton, offered her a deal: He would buy the house from her, but then he would rent it out to her so she could continue living there. The teacher accepted the offer and had a lawyer hammer out all of the details.

A month later, Thornton needed a helping hand himself. He went to the teacher — now also his tenant — to get a loan of $5,000. He must have seemed like a safe bet: A year earlier, he had borrowed from the teacher and paid back his loan in full. The teacher issued the loan and retired a few weeks later, in January 2010.

Today, the city’s Conflict of Interests Board announced that Thornton would pay a $3,500 fine for the transactions, which violated a city rule that bars employees from doing business with superiors or subordinates. Thornton accepted the ruling and agreed to pay the fine, according to a disposition the board released.

According to a press release, both the board’s investigative arm and a city office that looks into allegations of wrongdoing at schools, the Special Commissioner of Investigation, had worked on determining that the illicit transactions had taken place.

The Department of Education is not pursuing any further action against Thornton, according to a spokeswoman. The spokeswoman, Connie Pankratz, said the department considers employees’ conflicts of interest violations on a case-by-case basis and seeks additional consequences only if the violations also break department rules.

But sometimes, transactions like the one the conflicts board determined that Thornton had with the teacher he supervised do wind up costing school workers their jobs.

In one prominent example, the city moved to fire Jose Maldonado-Rivera, the founding principal of Columbia Secondary School for Math, Science, and Engineering, after city concluded that he had engaged in an “inappropriate financial relationship” with the school’s parent coordinator. The investigators found that Maldonado-Rivera had paid the parent coordinator to babysit his son and had allowed her to live rent-free in his home.

The offenses likely would not have yielded such harsh sanctions if they had been the only times Maldonado-Rivera had been cited for flouting department rules. But the department had placed him on a two-year probation just months earlier Special Commissioner of Investigation Richard Condon found that he had not sufficiently supervised a field trip on which a Columbia Secondary School student drowned. The probation meant that any offense would be grounds for dismissal.

Today’s conflicts ruling was not accompanied by a report from Condon’s office, nor has the office previously released a report about Thornton or M.S. 302. Condon publicizes only a fraction of SCI’s reports, even when allegations are substantiated.