Foster your student's group of friends. The most vulnerable kid in a school is the loner. Do what you can to keep your kid connected to his friends. Know their last names and where they live. Be able to get in touch with their parents.
Kids are good actors.
That nice, polite kid who visits your house may not always be what she appears. Give your child and the school your cell phone number. If you can't be reached easily at work, invest in a pager. Tape a quarter somewhere it will stay for emergencies only. Create a connection to another adult and make sure it works.