Summary judgment for defendant-school district in an action brought under 42 U.S.C. section 1983 by plaintiffs, a high school student and his father, after the student was temporarily expelled for sending violent and threatening instant messages from his home to his friends about planning a school shooting, where: 1) the messages presented a real risk of significant disruption to school activities and interfered with the rights of other students; and 2) under the circumstances, the school district did not violate the student's rights to freedom of expression or due process.