I went through the assessment centre (successfully) back in December and it was a relatively straightforward process, entirely as to be expected based off the materials provided by TfL Recruitment.
On arrival you're held in a waiting area with the other candidates, before being called through for the first stage, which is the individual role-play. Take note of all the information given to you and digest as much as possible - quite a few people who were at the centre when I was were caught out by this. Stay calm and stick to your guns and you'll be fine!
After this you move to a second waiting area and - gradually - the numbers will be whittled down as they send those unsuccessful at the role-play home. This can mean quite a long wait!
The second stage is the written assessments - there are three distinct phases and each of them are timed. They assess your numeracy skills, data interpretation skills and handwriting ability. Again, read each question carefully and take your time and you'll be fine; there are some good examples in in the literature provided by TfL and if you can find family or friends to come up with others for you to try that could be a benefit. All the information is supplied to you so there's no need to know anything in advance - although it does help!
If you're successful at the second stage the third and final stage is a one-to-one competency based interview - just like the phone interview for stage two, but this time in person. You can use the same examples as you did on the phone, but they'll want a bit more detail. There are also a few more questions asked - again, check all the info you had in your pack, it will be invaluable!
After that it's back to the waiting room to fill in various bits of paperwork and you're sent on your way - it can be up to a two week wait to find out if you're going to be offered a contract, although I was lucky and found out only a couple of days later - end result being that I'm starting my training in just over a fortnight.
In all, take your time, stay calm but also enjoy it - I didn't find it unduly taxing and it was a good opportunity to also talk to other candidates and ask a bit more about the job from the recruitment team. Best of luck with your application.
