More information is needed, but in a nutshell, it is possible that a student can be disciplined walking to/from school. Again, far more facts are needed.
Note: I am not licensed to practice law in your state. I simploy provide this response for general, information purposes only. This is not to be construed as legal advice and does not establish an attorney-client relationship. Consult appropriate legal counsel in your area.
You need to review the Board of Trustees policies for your school district, which typically you can find as a link on the school district's web page in the section for the Board of Trustees. It is not always easy to find so review the page carefully. You also need to review the school's code of student conduct.
While a lot more information is needed in order to provide you a more definitive answer, there are instances in which the school can discipline students for events occurring off the school grounds.
This is general information and should not be construed as legal advice. Without knowing the specifics of your situation and engaging in an attorney-client relationship I am unable to provide specific direction.