A federal appeals court has upheld a 20-year prison sentence for a former North Carolina teacher convicted of taking children out of state to have sex with them.

Jimmie Grubbs, who taught at a Huntersville middle school, pleaded guilty to 12 counts in 2006. He did not appeal his conviction but claimed his sentence was excessive.

A three-judge panel of the 4th U.S. Circuit Court of Appeals on Friday rejected Grubbs' argument that a judge improperly lengthened his sentence for additional offenses for which he hadn't been convicted. The court said a sentencing judge can consider "uncharged conduct" that's proven by a preponderance of the evidence.

Investigators believed Grubbs, now 69, may have sexually assaulted as many as 15 minors on campus and during trips to South Carolina between 2002 and 2006.