The inner workings of schools are highly scrutinised by the media, parents and politicians, and the highly marketised system puts parental choice and competition between schools at its heart
This means that there's a lot of secondary data about schools publicly available, often made by schools themselves
Data like exam results/league tables, truancy & subject choice figures, Ofsted reports, government inquiries and school policy documents
Schools themselves make personal documents like individual pupil reports
Schools are therefore data-rich, and sociologists can make use of the secondary data. However they may not be able to get access to school records as they are confidential
Other school data may have issues, like truancy figures being falsified to make the school look better, and the legal duty to record all racist incidents being sidestepped by downplaying what has happened to maintain a positive image
In the same way, official stats about exams should be treated with care as schools can change their curriculum to get better results, like entering pupils for lower entry exams