Sadly (or luckily for everyone else on the road) a US licence only lasts for 12 months in the UK...
I've no idea what people do in the bazillion lessons it takes to pass a UK test. Admittedly I only learned in an automatic, but go round corners, park, reverse, erm, that's about it. I read a book about road signs (in the US they vary by state, town, country etc., hence the endless quandary about turning on red) and rules (in most states exchanging gunfire with 'peace' officers is frowned upon*) so I could pass the theory multiple-choice. I passed first time though you could go back and try again after a two-week 'waiting period.' They've probably tightened things up a bit. That said, it is traditional for American kids to still learn to drive at school.
*in one recent (well 2012) case in Ohio, a backfiring car outside the courthouse led to a 62 car police chase (real life, not Blue Brothers) and the police, on finally cornering the perpetrators in a school parking lot, shot the car 137 times, one single police officer fired 49 rounds. The two people in the car were shot 23 and 24 times each. They'd committed no crime other than drive away from the scene of committing no crime. It goes without saying that no firearm – despite being 'seen' – was never found and the police officers mostly got away it, the two main officers involved eventually get fired. I don't think you need my help to guess the skin colour of the people in the car.