Why do you want virtual desktops??
Maybe we could have bit more information about your school.
Rough size and construction type
Do you have any fibre runs?? If so what type and how far are the runs?
What type of cabling do you have for data outlets cat5/5e/6/6a?
What switches do you have??
What are they used for?
How much storage do you have/need??
Where are students and staff files saved?
Do you have your own email services?
What is your backup solution?
Is this under your control??
If so what model?
How many phones
What applications are used??
Are there mobile classrooms? Or are laptops only for staff use?
Anymore information would be useful to help us help you
I'd be looking at the infrastructure to give the site a solid base - once the network and wireless has been brought up to standard then I'd be looking at what the pupils and teachers will be using. For the age group I'd be looking at something robust (ipads will shatter if dropped) so maybe a convertible netbook? Slots straight onto the Windows domain and stands a chance of making it if it gets knocked or dropped. They're good value these days and you could perhaps buy a class set and move them around in a charge trolley?
Have a look at this one Classmate 2S and a trolley from Laptop Security | Compucharge Limited | UK Laptop Storage solutions
What problems are they suffering?