The Child Welfare Information Gateway publishes a list of signs of possible abuse:
-Sudden changes in behavior or school performance.
-Lack of help for physical or medical problems.
-Learning difficulties.
-Overly passive, compliant or withdrawn.
-Stays at school as long as possible; does not want to go home.
-Detached from parents.
-Suicidal.
-Runs away.
-Nightmares and bedwetting.
See more at www.childwelfare.gov.