You may have a potential lawsuit on your hands against the teachers or school board. There is a duty of care owed by these groups when you leave your child with them. It is strong duty of care because that of the type of work they do. In essence, you entrust them to carry out to the task of keeping your child safe.
Since you are obligated to send you child to school to age 16 by the law then the responsibility falls in their hands while on-site or even on off-site school trips.
There are many questions that could be asked in terms of the measures they enacted and the type of safety policies they have in place. Did they try to mitigate against injury?
Their  duty is to protect against foreseeable risks and if they did not they you would be able to initiate a claim against them for damages including medical care as well as pain and suffering.