A woman convicted of witchcraft during the 17th-century Salem trials is expected to be pardoned thanks to a group of campaigning US schoolchildren.

Elizabeth Johnson Junior was sentenced to death in 1693 as mass hysteria about witches swept colonial Massachusetts.

She was granted a reprieve and died in her late 70s in the 1740s but, unlike other convicted witches, has never been exonerated.

When eighth graders at North Andover Middle School, near Salem, learned about her plight during their civics class, they decided to take action.

They carried out extensive research, studying primary sources to understand that Ms Johnson was targeted because she was unmarried and possibly had a mental disability.

"Part of our introduction to the civics class overall is based on the idea of identity, values, stereotypes and civil discourse," teacher Carrie LaPierre said.

"So looking at the situation regarding Johnson from this lens helped students develop perspective and empathy for her case," she added.

The 13- and 14-year-olds could not understand how Ms Johnson was overlooked for a pardon: she had no immediate descendants lobbying for it.

They began writing letters to local representatives and helped state Senator Diana DiZoglio draft a bill that will clear Ms Johnson's name.

Ms DiZoglio recently introduced the legislation, which is not expected to face any opposition.

More than 150 people, mostly women and including Ms Johnson's mother, were accused of witchcraft between 1692 and 1693 as Massachusetts was gripped by fear, paranoia and superstition.

Thirty, including Ms Johnson, were found guilty, 19 of whom were hanged. Massachusetts has formally exonerated the other 29, according to Senator DiZoglio.

The Witch Memorial in Salem

"It is simply time to finish the job and clear the name of Elizabeth Johnson Jr. once and for all," she said.

The students are receiving updates as their bill moves through the legislature and are enjoying the press coverage they are getting, including in The New York Times.

"In light of the present-day events that have consumed the attention of most over this past year, this project may seem insignificant, but the kids' efforts righted a long-standing wrong, and I want them to be proud of that," said Ms LaPierre.