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.