All the schools I attended would place an automated call to my parents if I was absent for a class or the day. Mid-Semester progress reports were mailed to my house for my parents to review. If a student fell severely behind, the teacher could request a conference with the parent.
Perhaps... perhaps this school did none of that (hard to believe). But on some level, the parent has to actually give a sh*t about their child and their education. Working 3 jobs or whatever is not an excuse to be an absent parent.
I'm close with several elementary school teachers, and we've had this discussion before. A parent that doesn't care at all, will nearly always yield a child that performs poorly, no matter how much individual attention the teacher applies to the child. Parents must be engaged in a child's upbringing - they are the primary role model for the child and are the only people that can enforce desired behaviors like doing homework instead of playing video games.