There are pieces of software which will allow you to reset the local admin password but if this is a schools laptop, I wouldnt reccomend it.
The username and password will be a domain one so someone will need to contact the schools IT department for them to reset it using Active Directory, you will then need to get the laptop connected to the schools network in order for the laptop to sync and login with the password which it has been reset too.
I seriously wouldnt try and bypass the local admin logon of a schools laptop, the owner will be in breach of the IT security policy and may be subject to disiplinary action if found out
I work in the IT department for a large local government department