Definitely keep documentation of all of your attempts to recommend ABA Therapy and other possible solutions. Parents do have the right to refuse services; however, if the student's grades continue to be affected by their behavior, progress in their education will be stifled. You do not want this to look like you allowed this to happen. I would save/print progress reports for the student on a weekly basis, and I would document the student's negative and aggressive behaviors for the week. One you start to build a correlation between the student's behavior and their lack of progress in school, you might have a better, well-supported case to make to his mother. Sometimes people need to see the effects on paper before they acknowledge that help is needed.

With this parent I would take it slow and use indirect approaches. Even though I know it hard to explain to her you are trying to help we also have to accept the limits we can go. Maybe call the parent in and see what concerns her. She probably wants to help her child but doesn't want to label her child or feels overwhelmed.

I would show the mom examples of other families that have utilized ABA. Tell her that helping her child with his behavior is to his benefit. Seeing positive results from other families that have gone through it may be helpful for her.

As a parent they have the right to refuse help. She will accept help when she is ready for it. By accepting help she is saying there is a problem and she is not ready for that. Continue to offer when it comes up but other than that you just wait it out.