5. Till what age must children in the United Kingdom study?

The text states that secondary school in Great Britain is for ages 11 to 16 or 18. This implies that compulsory education likely extends to at least 16 years old, with the possibility of study up to 18 in secondary school.

Answer: Children in the United Kingdom study in secondary school from age 11 to 16 or 18. The text implies compulsory study likely extends to 16.