Students who rely on Southern Rail trains to get to college have told Newsbeat strikes on the network leave classes "half empty".
Six day-long stoppages are taking place this month in a row over who should operate train doors.
It's the latest in a series of strikes that have been going on for a year.
One senior teacher's told Newsbeat there are now concerns "across the region" about pupils completing courses on time.
'It doesn't make anything easier'
Becky and Bailey, who are both 17, go to college in Chichester.
"During strike days it's literally not possible to get there at all so I have to rely on lifts from other people," says Becky.
"Obviously you're stressed because of exams and stuff, but you're also stressed about how you're going to get home and it doesn't make anything easier at all.
"On strike days I have to leave half an hour early to get the train, otherwise I can't get home. So I've lost four hours just from that one lesson alone."
But even if she does get in, she says classes are still disrupted.
"It has quite a big impact because obviously a lot of people in the class can't get to the lesson, so the teacher doesn't teach what they were planning to teach and we don't cover the right amount of stuff."
"A level courses are pretty tight anyway," Bailey adds. "You're often looking to finish the course one or two weeks before the exams, so every time half the class is missing because of trains, it really puts on pressure for revision time at the end of the year."
But he also thinks the strikes have a deeper impact.
"It makes you less motivated because you spend a lot of time travelling to get home, a lot of time getting into college, and when you get back you're worn out."
Callum Macleod goes to college 60 miles away in Hastings, but says he has the same problems.
"When I turn up and find half the class isn't in, it really puts pressure on me.
"If there's no way for A-level students to get into college on time for exams then it could potentially ruin their future career and set them back a year, which is unacceptable."
Other students from across the south have been shared similar stories of frustration.
"We're seeing a really big impact on not only attendance but also student welfare in terms of tiredness and their ability to cope," says Jim Sharpe.
He's the vice principal at Sussex Coast College in Hastings.
"There are concerns across the region in terms of being able to complete courses and cover everything that needs to be covered."
His college has started putting on replacement buses to help students get in.
"Bluntly, the cost to the college is around £500 a day. So, to date, the cost is approaching £10,000.
"We need to protect the money we would be spending on students in terms of resources but eventually this is going to have a serious impact on college finances.
"The biggest concern for all of us is that the expenditure on the coaches will mean we can't do things for students, and it's ultimately going to impact on the quality of their education."
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