The newspaper looked at land transactions from 2004 to 2008.
In the case of the land for North Gwinnett Middle School in Sugar Hill, the AJC found a developer bought the land for just under $6 million in 2004, and the next day, sold it to the school system for about $1 million more than he paid.
"It's much worse than I ever thought," said resident Joe Newton.
He's urged the district attorney to look into land deals in the county.
A grand jury investigation into the land deals with the Board of Commissioners led to the chairman's resignation and the indictment of one commissioner last year.
As for the school land deals, Newton also wants an inquiry.
"People don't just tie up this much money, millions and millions of dollars, unless they've got a ready buyer," said Newton.
A spokesperson for Gwinnett County Public Schools says the system's land acquisition process works and has actually saved taxpayer dollars.
"We don't communicate information on which pieces of property we're looking at," said Sloan Roach with Gwinnett County Public Schools.
She says the transactions happened in the boom times of real estate, which was also a time school enrollment was increasing and the district needed land.
"If it was a big piece of land (developers) probably knew the school system, especially if it was in a high-growth area, might be an interested buyer," said Roach.
She also noted that the school system had to negotiate with developers if the land owner already had an existing option or contract.
In another case, the AJC found a developer bought land near Dyer Elementary School in the Dacula area in 2005 and sold it to the school system the same day for $1.1 million more than he paid.
Channel 2 Action News called Gwinnett County District Attorney Danny Porter to ask if he will look into these deals, but so far there has been no response.