Many students will require further time in order to continue their studies in the UK once their entry clearance visa expires. Some students will require extra time to complete their current course of study, while some will want to take up a new course of study once their first course is complete.
Making a Tier 4 (General) Leave to Remain Visa Application in the UK
UKCISA - Your family's immigration
PBS Dependants Policy Guidance-Policy Guidance for PBS Dependants