I always learn things from listening to the radio. On 'The Infinite Monkey Cage', I heard Brian Cox rattle off a 'rule of thumb', which goes something like:
A number plus or minus the square root of the sample size is consistent with random sampling error.
https://www.bbc.co.uk/programmes/b04yfsst (listen from 20 minutes in)
I hadn't heard that one, but deploying those key research tools, the back of an envelope and a pencil, I could see where it comes from.
SHEU surveys are featured in the Public Health England toolkit for schools and colleges, put together by the Anna Freud Centre
The toolkit encourages schools and colleges to monitor their pupils' and students' mental wellbeing, and offer SHEU among other approaches to doing this. Of course, a SHEU survey includes other aspects of health and wellbeing than mental and emotional.