I used to do these for volunteers in our school till last April, the enhanced check which is needed for schools was taking almost 4 months last time I did one. The older one was quicker I am not certain but I believe it is still attainable but you will need the enhanced one for school..became a must after the two little girls were murdered by a school caretaker id 2000/2001.Cost for enhanced was 35 UK(sorry my laptop doesn't do a pound symbol). I would expect the school to pay for it. I think the school head can at it's discretion employ while it is being done but has to ensure that the employee will never be alone with kids..bit difficult for a caretaker who is often there after hours, but he/she might do it.
One bit if advice, do EXACTLY as it says on the form, eg use black ink pen, and make sure you go back 5 years, my husband John applied for one as a school volunteer, and put his previous addresses for five years except 6 days which was at a point when we moved, they sent it back to get it updated with the missing 6 days which was the back end of 5 years,and I have known them sent back for blue ink, not in block capitals etc, so have a spare and be careful, read all the instruction leaflet that comes with it carefully.. the school will have the forms.
XX Jeannine