dysteachia

In a well-publicized paper that addressed why some students were not learning to read, Reid Lyon (2001) concluded that children from disadvantaged backgrounds where early childhood education was not available failed to read because they did not receive effective instruction in the early grades. Many of these children then required special education services to make up for this early failure in reading instruction, which were by and large instruction in phonics as the means of decoding. Some of these students had no specific learning disability other than lack of access to effective instruction. These findings are significant because a similar dynamic is at play in math education: the effective treatment for many students who would otherwise be labeled learning disabled is also the effective preventative measure.
Mathematics Education: Being Outwitted by Stupidity by Barry Garelick

The effective treatment for many students who would otherwise be labeled learning disabled is also the effective preventative measure.

and see Galen Alessi's classic: Diagnosis Diagnosed