What are the criteria for changing custody and best interest of the child? Is custody changed if the child is in a stable home?

For your ex to modify the parenting plan he has to make a showing that there has been a substantial change in circumstances for the child or for you (NOT him) and that the benefit of change outweighs the harm of change AND that 1: you two agreed to modification, 2: You've let her live with him already OR 3. The child's present environment is detrimental to her health, safety or welfare. I linked the actual statute below. Look at sections 1 and 2.

I assume that he would focus on the child's academics. All you would have to do is get documentation from her school showing the efforts to deal with her learning issues, health care records showing you efforts to have her ADHD treated in an appropriate manner, and statements from family, friends and others who know you as a parent. Obviously, if you have documentation about the ex's anger still being a problem then use it. But modification is NOT an opportunity to re-litigate the divorce!

You could do this yourself, but if the ex has the money to make it a contentious mess, you'd be better off hiring an experienced family law attorney.

By the way, if it's been more than 2 years since the last order of child support was entered, why not get child support modified at the same time. Considering dad's new-found devotion to his daughter certainly he would want to pay child support consistent with his current income?

Best of luck to you!