Under-18s in full-time education are now able to travel for free on London's bus and trams.
Thousands of people can benefit
To be eligible, the teenagers need to live in a London borough and be studying for at least 12 hours a week or be on an unpaid training scheme.
They also need to apply for a specific Oyster photocard when their school or college reopens.
In April, London Mayor Ken Livingstone made Tube travel free for under-11s and has waived bus fares for under-16s.
The mayor said almost 130,000 16 and 17-year-olds living in London could benefit.
He said: "It is a huge boost for individuals striving to fulfil their full potential through continued studies and will greatly help those who might be at risk of having to drop out of education through lack of money.
"This move also continues the policy of promoting the use of public transport wherever possible which is helping to protect our environment."