Schools take different approaches to how they collect, write and edit personal statements. If you are in charge of submitting the final references it is worth understanding the common weaknesses that result with each approach.
Approach: provide a general introduction to the school with individual tutors commenting on academic performance
Weakness: often fails to give insight into the personality of the applicant and their suitability for the course. Also the different styles can mean information may be difficult to access, for example predictions are included throughout the text.
Approach: Whole references written by a single subject tutor who knows the student well.
Weakness: Often does not provide sufficient information on all the student's subjects.
The most successful approach seems to be where individual subject tutors provide in-depth information, which is then incorporated into a reference that is written by one person.