Yes, unfortunately the Education Code states that acts while on school grounds or while going to/coming from school can be the basis for an expulsion. If he was intoxicated on school grounds, that is likely enough. There may be arguments, however, surrounding the time of day, the relation of this act to school activity/attendance, etc.
It is very important you hire an education attorney to help you resolve this matter in your son's best interests.
Michelle Ball, California Education Attorney for Students since 1995
http://www.edlaw4students.com
