My daughter has lived with her mother in Tampa, FL for the last 14 years since we divorced. She had a number of social problems and wanted to change primary residence to live with me in Palm Beach County, Florida. She moved in with me May 2011, enrolled in school and completed her junior year with me. I have automatic deductions taken out of my paycheck as child support sent directly to her mother. Her mother and I agreed that she would send me back the child support and match the exact amount I pay (its minimal since we divorced 14 years ago). We chose not to make an official change in primary residence with the court as neither one of us wanted to incur legal expenses. However, since that time, she has only returned a portion of the child support and owes me about $3,000. My daughter visited her mother this summer and is now deciding to move back in with her mother. Her mother is now threatening me with going back to court to seek an increase in child support (keep in mind my daughter is now 17). Question: Will the court recognize the amounts the mother owes since the child was officially and induspitably living with me for the last year (she registered and completed her junior year in my town)?

Maybe. Maybe not. That's the risk you assumed by doing it unofficially.

My opinion is probably not. As far as the court is concerned the mother is and was the custodial parent. And the court will look at whatever you did outside the court as not having happened.