Tardy Boy

I have a student, Tardy Boy, who is - I bet you'll never guess - always tardy! He has my class from 8:30 - 9:10. Tardy Boy isn't just a little late, he strolls in around 9 or 10. Every day! Of course Tardy Boy is struggling in reading (or he wouldn't be in my class), but he is one of my lowest students. He's in 2nd grade and doesn't know all his letters, much less what sound they make. I don't know how to get him to school. His mom has been to court, I've talked to her about the importance of my class, principal and assistant principal have talked to him, I reward him for showing up on time, I've kept him in from PE for being so late, and I'm out of ideas. She promises to get him here, but doesn't. Just for an idea of how much he misses my class, in the last 15 days of school he has missed 7 times and been late another 5. So 3 days he was on time. He has been less tardy this week, but still about 45 minutes late for school. Tardy Boy is so frustrated in his class because he is so far behind. I'm so frustrated with this parent. Last year she withdrew him for about 3 weeks. He didn't go to another school. He was helping clean the house. WHAT?? But yet mom says she's concerned about his progress. Argh. Any ideas are welcomed!