Absenteeism matters. It is more strongly associated with dropping out than low test scores. The reasons that children from low-income families miss more school are varied. Their families may not have the ability to advocate for proper services for students with learning or physical disabilities.
The response to this week's big report from the National Council on Teacher Quality has shown that not every district agrees on the definitions for excused absences, and that efforts to curtail them are having little effect.