I attended the 'grammar stream' open morning yesterday and was really impressed by the teaching and by the behaviour of the students.
Our tour group made a point of deviating from the planned route in two buildings and walked along corridors where there were attentive, orderly classes on both sides.
One teacher whose Maths lesson we observed briefly from the doorway came out to explain that her small class of well-behaved kids were 'bottom set' - presumably to clarify why they were doing their 7 x table. She had an Assistant helping out which I thought was very good. I'd have been very happy with the set-up if my DC were needing remedial support.
The management and student presentations following the tour were quite good. More useful was the opportunity to talk afterwards to some of the current grammar stream students. There was a lot of praise for the quality of the teaching and individual support. When pushed for a critical analysis, the quality of supply teachers was mentioned as a problem, but I don't know how that compares with other schools. (I suppose there is also a follow-on question for the school to find out the level of teacher absenteeism.)
According to our Year 9 tour guide, there is good deal of movement to and from the grammar streams , including in-year, with regular assessment. The 'top' grammar stream, who have passed the 11+, are guaranteed their places for three years; the middle and lower grammar streams are subject to review, and children who start off outside of the grammar streams altogether can move into it if they show sufficient aptitude - one difference being that the grammar stream completes KS3 in two years instead of three.
Our guide said she had joined in the 'middle' grammar stream, for children who narrowly missed passing the 11+, but has this year moved into the top set for English, Maths and Science. (I don't have a handle yet on how subject setting works in relation to streaming at Knole: does anyone know?)
It's a pity that Knole offers a smaller range of academic subjects than some schools, eg French is the only foreign language; but I would favour it over Trinity for 2016 entry for my DS unless my impressions visiting both again next year are vastly different.