"No teacher worth his or her salt wants to leave a child behind."
Every teacher has a limited amount of time, ability, resources to work with, student abilities and attitudes, etc. with which to work. Given these constraints, is her attitude ignoring reality? You may not want to leave a child behind, but if it's a choice between getting one student up to speed while 29 other students in the class languish in boredom, maybe leaving one child behind is the best alternative. The opportunity cost of helping one student is hindering the progress of 29 others.
I think the problem all goes back to the fact that we operate within a one size fits all educational system. Create more variety in terms of class options, vocational programs, eliminate most restrictions on child labor and wages so students can learn by doing and eliminate compulsory attendance laws and education improves by being better able to better serve the variety of individuals who seek education or training.
I'm not holding my breath.