Amillion - they must by law have plans if they have any asbestos on site (or even just suspect unknown materials I believe.)
The thing is, I don't think they are going to fess up to non-compliance to a parent, or anyone else for that matter. Why would they tell you the truth? If they don't keep up with mandatory surveying etc, they are hardly likely to bat-an-eye at telling you its all up todate to my mind. 
I would ask to see the actual register etc and see what they say.
Fiona - I understand. The problem must surely be, that for some schools the mandatory testing is seen as too expensive for the value it brings. Its not right, but again, I wouldn't know the solution to the problem.
Some local authorities are rigourous in their testing tbf. ExP has been to schools where there has been very little asbestos on site - possibly a minute amount in a below ground boiler room only - but still his firm returns year in year out to fully examine the entire site. This is not at all cost effective -and so some areas just skip over the legislation. There needs to be a more reasonable middle ground.
As has been said - asbestos is perfectly safe when managed correctly. Bear in mind that the people who know about the asbesos in schools are invariably those that also work in that place. They don't want to get asbestososis or mesothelioma themselves and are unlikely to be making decisions that will expose themselves to it as much as pupils etc.
Does that make sense?
Also, I must re-iterate that control of asbestos in the UK is super vigilant in comparison to elsewhere in the world. You are relatively safe here. You are in fact, more liable to come into contact with it in a domestic setting for which there are currently no controlling regulations.
Ripping out an old sink, removing an old shed or garage, taking out an old fireplace - all likley to contain asbestos and many diy'ers simply plough ahead without any knowledge of safe removal and disposal 