Under Washington child support laws is a parent still responsible for child support if child drops out of school at age 16?

Yes. Child support is usually paid until the child reaches majority (18 years old) or finishes college if he or she is attending school. That provision is usually agreed to by the parents at the time of the divorce. You should check of course with a family lawyer handling support cases in your home state.

Good luck.

Having worked for WA child support for 10 years, I can say the previous post is wrong. Almost all court orders specify support to be paid until the age of 18 or graduating high school, whichever occurs last. If a child drops out of high school before the age of 18, child support would terminate (arrears if any would still be owed).