The UK’s biggest teaching union has called for all private home tutors to face criminal record checks before being allowed to work with children.
The National Education Union (NEU) said teachers barred from classrooms may try to work as private tutors.
Research by the Sutton Trust charity suggests the number of children in England and Wales who received tuition has doubled in a decade.
The government said parents could carry out a range of checks on tutors.
A minister said families could check the outcome of misconduct panel hearings.
It is estimated more than 350,000 secondary-aged school children have received private tuition in 2018, according to a survey commissioned by the Sutton Trust, up from about 160,000 in 2009.
One in three children said the extra private tuition – where a parent has paid for the child to have additional academic teaching on top of their lessons at school – was to help with their GSCE exams.
It is thought there are up to 100,000 full-time tutors in the UK, according to the Tutors’ Association.
Unlike classroom teachers, tutors do not have to undergo a Disclosure and Barring Service (DBS) check before working with children.
Teachers are subjected to an enhanced DBS check, which determines whether they have any previous criminal convictions or have been barred from working with children.
In May, 49-year-old Sanjeev Mittal, from Birmingham, was jailed for five years for abusing two girls during home school lessons.
Parent Aliceson O’Beirne, from Leeds, said she was shocked to discover tutors were not regulated like classroom teachers.
“I employ a tutor to help my daughter Eve and I think it’s incredibly important that everybody working with children should have the appropriate checks.”
Ian March, from the NEU, said: “It’s important that tuition is not an unregulated industry.
“It’s absolutely vital that the government makes sure everyone who works as a tutor has a DBS check as people may work as a private tutor when they’ve been barred from working in other teaching environments.”
Labour MP Rachael Maskell said she was alerted to the legal loophole after a teenage constituent said she had been groomed for abuse by a private tutor.
The York Central MP said: “There is a real concern that anybody could turn up as a tutor and enter somebody’s own home, or be in a one-to-one relationship, with a vulnerable young person.
“I think the risks are enormous and we now need a proper process around this.”
Adam Muckle, president of The Tutors’ Association, the UK’s only professional body for tutors and tuition companies, backed the call for a change in the law.
“The Tutors’ Association asks all its members to have DBS checks as well as checking their academic qualifications,” she said.
“Our tutors also have references and testimonials as well as being signed up to a code of conduct.”
Minister for Children and Families Nadhim Zahawi said: “Nothing is more important than the safety of children and if parents decide to employ a private tutor for their children they should assure themselves of a tutor’s suitability beforehand.
“There are a range of checks parents can carry out, including checking the outcomes of the teacher misconduct panel hearings to see if a private tutor has been prohibited from teaching.”