If you are experiencing students who are ill-prepared for your classes, to what extent are you working with the teachers who send them to you?
In business, the concept of quality control as espoused by Deming (?) suggests the need to communicate with your suppliers so that you can ensure that the raw materials (or partially manufactured goods) are delivered within certain limits of variation.
I come from an industry background, where I was responsible for designing quality control systems. Why, in education, do we not keep statistics on abilities of our incoming students? Why do we not keep statistics on the amount and kind of learning that our students experience? What the types of performance variation exist? What are the sources of variation? Why are our insights not based on statistics that _we_ keep? (Perhaps we should be using our statistics students to help us design, and maintain such capabilities. Perhaps we should be using statistics students at local colleges and universities to help us with this important work. Perhaps we should be using local teaching universities to help us with this effort.)
The district in which I previously taught, the high school teachers met several times a year with the middle school teachers to consider ways that their students could be adequately prepared. I don't know if they worked with elementary teachers.
In my personal opinion, there is too little dialogue between teachers within a school, and between schools to ensure that the 'products' we receive and the 'products' we produce are of sufficiently good quality (low variation).
Please excuse the dehumanized types of references.