Mina Shaughnessy understood that there was a pattern of errors in her students' writing and that figuring out those patterns communicated something larger about how they write, and more importantly recognizing the reasons and the patterns of those errors could help teachers to identify ways to help students improve their writing. 

Shaughnessy insisted that students who came to her writing classes had already developed strong and “dynamic” language skills, they just lacked the knowledge to translate that into discourse appropriate for a college paper (Shaffer 24).

By 1975 Shaughnessy had collected thousands of samples of student writings and compiled notes, observations, and questions about them in a giant three-ring binder.  Errors and Expectations which was published in 1977 and was a roaring success.

Errors and Expectations is still considered the source for modern Basic Writing paradigms and is credited with shifting the previous beliefs in teaching that basic writing students are simply not as bright as other more advanced students – only that their background has not been as privileged, and that it is the teacher’s responsibility to guide their students toward developing better writing skills.

In a way it was through Shaughnessy’s work that teachers were encouraged to rethink their old methods and become students themselves by learning to better identify and teach to their student’s needs. Errors and Expectations showed them that students with writing deficiencies weren’t incapable of writing- they are merely unskilled- new to the task, and it was the teacher’s role to encourage students to discover the language that was already in them and develop that person into a better writer.  

Shortly after Errors and Expectations was published, Shaughnessy was diagnosed with bladder cancer, and sadly she died just over  a year later. (Maher 106) 
The Mina P. Shaughnessy Prize was created in 1980 in her honor and is awarded annually for "outstanding scholarly publications in the fields of language, culture, literacy, or literature with strong application to the teaching of English.