If students can't use magic outside of Hogwarts, how are they meant to practice spells for subjects like Charms, Transfiguration, Defence Against the Dark Arts?

It's stated multiple times in the books that it is forbidden for underage wizards to use magic outside of school. So how are they meant to practice their spells and wandwork during the holidays? I can understand 1st-3rd years not practising wand magic and spells in the summer holidays. But surely 4th-7th years with upcoming OWLs and NEWTs would need to practice spells for their exams? And Hermione in the first book says that she's done a few spells at home. She's Muggleborn so how did that work?