All the possibilities I've seen mentioned apply to “Local Network” installed MIS Systems as well. If anyone within the school wants to hack the systems, they can...
There are many ways to make sure that cloud systems are secure, and systems are protected from attacks. Any certified (ISO/etc…) Data Centres have such securities in place anyway.
Cloud computing security - Wikipedia, the free encyclopedia
Also further security should come via MIS systems with user accounts. Like “Windows Accounts” do:
Implement a strong password policy
Force users to change their passwords in a given frequency (weekly/monthly/etc…)
Lock accounts temporarily after a number of unsuccessful login attempts
2-level authentication