We don't know what's going on with the school, only that the juvenile charges have been dropped. That does open up the possibility for a common law false arrest suit against the deputy and a suit under federal law for deprivation of civil rights (which allows an award of attorney fees).
Sometimes when charges like this get dismissed by agreement with the prosecutor, it is done with a stipulation of probable cause. The person arrested stipulates the officer had probable cause to arrest. This is done to keep from exposing the officer to civil liability. I personally think this borders on unethical behavior on part of the prosecutor because it is unethical to use a pending or threatened criminal action to gain an advantage in a civil action. We don't know if there was a stipulation in this specific case.