A full-scale rescue operation was launched after seven college students on a night-time orienteering trek became worried by a herd of cows.
Emergency services were called out on Monday night after the teenagers became stuck on a hill near Swanage, Dorset.
The girls from St Albans had been tasked with using map reading skills to find their way to the nearby adventure centre they were staying in.
A Loreto College spokeswoman said the task was run by an "experienced team".
The teenagers, aged 14 and 15, were on the residential field trip as part of their geography coursework.
On Monday night, they were dropped off about three miles (4.8km) from the centre and asked to find their way back.
They were given mobile phones and emergency numbers in case they got into difficulty.
They contacted the centre when they came across the field of cows and coastguard, police and ambulance crews were sent to the scene, a Hertfordshire County Council spokeswoman said.
"They got to the field and realised they needed to be on the other side of it and did not want to go through it," she explained.
Maire Lynch, the head teacher of the college, said: "One group of seven girls became concerned and used their phones to call for help from the centre, as instructed.
"The centre began to direct the girls home and a member of centre staff went out to join them.
"Last night's activity was run by an experienced and established team. "
No-one was injured but one teenager who complained of feeling cold was taken to hospital to be checked over by medical staff.