My son is at Harris Westminster 6th Form, he finishes on Friday!
It has been the best ever choice and he has thrived for the two years there. The teaching is excellent and does more than just teach to the exam, the students are inspired to think beyond.
The tutoring and pastoral care has also been excellent including the support for his UCAS applications.
My son went a bit overboard in year 12 and joined every club and society possible, but managed to cut back a bit in year 13. He has especially enjoyed the Societies teaching, access to lectures at Westminster, choir and orchestra. Also running, tennis and badminton.
Things to be aware of:
Expectation that they will do 4 A levels
Saturday school - from summer term of Year 12 through to June year 13.
Lots of testing - "welcome back exams" very half term etc.
Commuting into London during train and tube strikes can be tricky
Temptation to buy expensive lunches every day
Overall, he would say that this last 2 years have been amazing and he is now ready to go to university.