Hi, I've been asked to quote a school and worked out the outside price, but they want a quote for just 'spot cleaning' or removing fingermarks, marks etc. for insides. Any ideas on pricing for this compared to outsides? 
It's OK to quote for spot cleaning IMO if it is being carried out along with a regular service - e.g. weekly outside cleans plus weekly spot cleaning inside with a full clean every few weeks. However, with a school, it's likely that it is cleaned at much less frequent intervals (often 3 times a year during end of term breaks). Therefore, I would say that the interior windows are not really appropriate for spot cleaning. Even if you did this, the infrequent intervals would mean that there are so many spots to clean, you might as well do a full clean anyway.
If they want to save money, maybe the way forward is to offer 3 times a year on the outside and once a year inside. It probably wouldn't cost them as much as 3 inside spot cleans.