Always good to stay until Year 13 (17-19 years), rather than leave at Year 11 (15-17 years). That way you can do your sixth form. In fact, the government are enforcing a new law, stating that children must attend secondary school from Year 7 up to Year 13. They will not be enforcing it now, however, but they will be in a few years. This will probably only affect today's Year 7s and Year 8s.
which country's government