flying school sign each page of student log books as they are filled in.
There is no requirement for this however:
AMC1 FCL.050 instruction time:
a summary of all time logged by an applicant for a licence or rating as flight instruction, instrument flight instruction, instrument ground time, etc, may be logged if certified by theappropriately rated or authorised instructor from whom it was received;
So if the FI has not endorsed it the NAA can refuse to accept it.