Short-term students without prior entry-clearance should avoid arriving into the UK via the Republic of Ireland. Please refer to this chart in our visa instructions to help you decide which visa route is appropriate for your circumstances.
The UK and the Republic of Ireland are both part of the Common Travel Area (CTA). The CTA streamlines arrival from Ireland for most travellers, but because there is no immigration control on arrival in the UK it can cause problems for students.
Students who are citizens of the USA, Canada, Japan, South Korea and other non-visa nationals who are planning to travel to the UK without applying for a visa beforehand,
If you arrive in the UK via a connecting flight in the Republic of Ireland (i.e. Dublin, Shannon, Cork, etc), you will NOT receive the appropriate immigration permission to study in the UK for the semester. This is because there is no immigration control in the UK if you arrive directly from Ireland and Irish immigration officials will not provide you with permission to study in the UK. Note that any immigration permission you are given on arrival in Ireland is for Ireland only, not for the UK.
You should therefore plan to fly directly to the UK, rather than via the Republic of Ireland.
If, despite the above advice, you do enter the UK directly from Ireland without specific UK immigration permission, you will be asked to leave the UK prior to beginning classes and enter a country outside of the CTA (for instance France), and then re-enter the UK so that you receive the correct stamp in your passport. It is your responsibility to arrive in the UK correctly; failure to do so may jeopardize your studies in the UK and will require you to incur additional travel expenses and stress.
Questions about this should be directed to the Office of Global Services (email@example.com; 212-998-4242).
Note that there is no problem for someone who has applied for a UK Tier 4 Visa or Short-term Student Visa before traveling. If you have a UK visa in advance, the visa will not be date stamped on entry to the UK, but this is fine. You should keep evidence of your travel in case your date of entry ever becomes important or relevant. Furthermore, if you do travel and re-enter the UK later, for example for a short trip elsewhere in Europe (other than Ireland), your entry clearance will simply be date stamped on re-entry.