What makes you think the blame falls on teachers?
Because, it is the job of the Teacher to teach.
In every individual School, there are Teachers who Pass students who do not achieve the Standards which are said to be in place.
Therefore the burden of Educating a child who is NOW behind in learning falls upon the next Teacher in the next grade.
That Teacher does not have the time necessary to Educate that Student who is lacking certain skills in a subject.
Therefore the Student falls further behind in said subject-(s) but then again the Student is passed on to the next highest Grade, where he will end up at the end of that year even further behind than he was.
We have a Production line going in Education, the System cannot take or afford the time it would actually take to insure EVERY Student achieved the Standards set.
There is a built in Failure rate that is acceptable in the System, it isn't that the Students in that category are stupid, it's that the System (Production line) had to keep moving for the greater number to Graduate, regardless of their individual abilities.
Therefore like it or not there are Students Graduating who cannot write in Cursive, and use a pencil and paper to figure out a Math Problem.
No every Student who enters the School System needs to Graduate and go on to Collage.