Not necessarily.  If you child attends college, or if your child lives with one of you and is principally dependent, then the child support obligation may continue until your child is twenty-one or even twenty-three.  You’ll find the full text of the statute at Massachusetts General Laws Chapter 208 Section 28, and the relevant part reads:

“The court may make appropriate orders of maintenance, support and education of any child who has attained age eighteen but who has not attained age     twenty-one and who is domiciled in the home of a parent, and is principally dependent upon said parent for maintenance. The court may make appropriate orders of maintenance, support and education for any child who has attained age twenty-one but who has not attained age twenty-three, if such child is domiciled in the home of a parent, and is principally dependent upon said parent for maintenance due to the enrollment of such child in an educational program, excluding educational costs beyond an undergraduate degree.”

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