We have middle schools and I have found the system to be excellent. Our LA has 2 middle schools (only) in our corner of the borough. First school is YR- Y5; Middle school is Y6-Y8 and High school is Y9-11 (the school also has a 6th form).
Middle school A has 21 feeder first schools; middle school B has 20 feeder first schools. Both middle schools feed into 1 high school. It’s a large rural catchment. Some of the first schools are very small.
What works well, is that by Y5, both my dc were getting a bit fed up of hanging out with 4 year olds and were ready to move on, but the jump to middle school was far more relatable than going to secondary school. Lots of people had older siblings there, and the middle schools host so many sports events, quizzes etc (as well as being hired out for holiday clubs and for their sports pitches) that there are very few children who are unfamiliar with them when they go for their transition week.
The middle schools are as nurturing as primary schools, but work on the secondary school model of moving round subject classes. Both DC blossomed in maths once they were taught by subject specialists! And of course, middle school keeps them apart from big, smelly teenagers until they are one, but gives pupils lots of growth opportunities and leadership roles. Our particular middle school had very strong links with the county music service and local grassroots sports clubs and worked with them to develop many extra curricular opportunities.
The slight downside is that the middle schools have 2 terms to get Y6 through SATS. They tackle this head on, with maths and English every morning and other subjects on the pm of Y6.
Then, in year 9, just when you really need to start taking school seriously, you’re off to high school. Without younger years, the high school can really focus on exams.
Some people think that changing schools twice would be disruptive, but - as mentioned above with the middle schools - the high school music, theatre and sports facilities are heavily used by community groups, so kids are very familiar with the buildings (and some of the staff) before they move on.
I won’t be too rise-tinted and say that there are no behaviour problems, but there are no particularly excessive behaviour problems, and they seem pretty thoroughly dealt with in school (I suspect the rural catchment helps, because everyone quickly disperses off on their once-an-hour or special-service buses home rather than hanging about after school)
For us middle school has worked very well. Two smaller changes at 10 and 13 seems more manageable than one big one at 11.