There is an 8 week service standard for normal Tier 4 applications.  If your application is made outside of peak times then it may only take 2-3 weeks to process, but if you applied during peak times it may take the full 8 weeks.  If your application falls outside of the 8-week standard period, please contact the Visa & Compliance team on visa@yorksj.ac.uk end they will follow this up with UK Visas & Immigration for you.