The biggest worry for most schoolchildren is homework and detentions, but for kids in Australia, sharks are becoming a much more serious problem.
The weather in Australia is so hot that kids often leap into rivers to cool off, but now they've been warned not to.
Sharks spotted by fishermen
That's because sharks are swimming up rivers in search of food after a really bad drought has left their normal hunting grounds short of fish.
A fisherman spotted a bull shark 25 miles upstream near a village called Wingham, forcing schools to warn their pupils not to go for a swim in the river.
The bull shark is one of the most dangerous kinds of shark and has been known to go after people rowing in Sydney harbour.
A second fisherman, a few miles downstream from Wingham, said he caught a 2.5 metre long bronze whaler around a week ago.