Congraulations to your DS, @hihi17 . My DS entered Whitgift at 13+, and we are very, very happy with the school.
They have 2 forms of boys (around 45) joining in Year 9 which stops the new joiners feeling quite so much the odd man out - important as there are around 250 boys in Year 9. The school has quite a broad range of academic ability, but the top sets are very strong indeed and talented boys are catered for well. There is a good range of academic subjects, and once they are in 6th form, having the option to choose IB or A levels gives good flexibility. The Learning Support department is very on the ball with regard to help with study skills and exam access arrangements.
Sport is a big deal, and there are lots of teams in each year group so plenty of opportunities to play even if not A team material. Be prepared for weekend sport to trump other commitments, with limited ability to opt out due to pre-existing commitments. However, according to DS there are plenty of boys who aren't sporty but who get along fine and there doesn't seem to be a social stigma attached to being non-sporty.
They offer a great range of extracurricular activities in addition to sport. Music is good (though not as strong as Trinity), and drama is excellent (and school productions often involve girls from other Croydon schools). CCF and DofE are popular. There is a long list of afterschool and lunchtime clubs, and lots of academic enrichment activities like visiting speakers.
It is a large school and communication from senior leadership can feel quite corporate. However, I like the headmaster and the vision he has for the school. We've had excellent communication from subject teachers and form tutors, and the communication and support leading up to public exams was very well-organised.
I think it is a school that suits energetic boys and robust personalities. From DS's descriptions, the teaching staff seem fairly tolerant of lively classrooms, but still have high expectations of work ethic and achievement.