attendance

I am a Tier4 student doing Master course in a University. I was told 100% attendance is compulsory. I have kids and was wondering what happens if you really have to take a day off for some emergency. Will they just ask visa department to cancel our visas. How long do they generally wait before contacting ukvi.

You need to ask your Tier 4 sponsor about this. They devise their own attendance and monitoring procedures and policies.