A long-standing Texas law that has sent about 100,000 students a year to criminal court — and some to jail — for missing school is off the books, though a Justice Department investigation into one county's truancy courts continues.

Gov. Greg Abbott has signed into law a measure to decriminalize unexcused absences and require school districts to implement preventive measures. It will take effect Sept. 1.

Reform advocates say the threat of a heavy fine — up to $500 plus court costs — and a criminal record wasn't keeping children in school and was sending those who couldn't pay into a criminal justice system spiral. Under the old law, students as young as 12 could be ordered to court for three unexcused absences in four weeks. Schools were required to file a misdemeanor failure to attend school charge against students with more than 10 unexcused absences in six months. And unpaid fines landed some students behind bars when they turned 17.

"Most of the truancy issues involve hardships," state Sen. John Whitmire, D-Houston, said. "To criminalize the hardships just doesn't solve anything. It costs largely low-income families. It doesn't address the root causes."

Only two states in the U.S. — Texas and Wyoming — send truants to adult criminal court. In 2013, Texas prosecuted about 115,000 cases, more than twice the number of truancy cases filed in juvenile courts of all other states, according to a report from the nonprofit advocacy group Texas Appleseed. An estimated $10 million was collected from court costs and fines from students for truancy in fiscal year 2014 alone, the Texas Office of Court Administration said.