Grammatical nit-picking

See this photo and others at The Huffington Post.

I was conversing with a young professional in academia a few days ago. The topic related to and English program, no less. A question was asked; by whom, I do not recall. Out came a wonderfully grammatically "incorrect" phrase:

"I'll try and find out..."

For those of you who may not see the problem. The "correct" form should be, "I'll try to find out..." Think about it: Was the speaker going to try something and find out something? No. The speaker was going to make an attempt to do something: try to do. Yet the try and form is quite widespread, and few notice it when used in conversation. Therein lies the problem which leads to the topic of this post: Does focus on "correct" grammar during assessment disadvantage English language learners (ELLs).

Of course grammar is a necessary component of language assessment, and I have called a "grammar nazi" more times than I can count. Nevertheless, one must keep in mind that "correct" grammar is not always a matter of rules but of conventions. That is, English includes many grammatical conventions that do not precisely correspond to rules. Often these are referred to as exceptions. Or in this case, what native speakers say and understand in actual practice is different from what is considered "correct".

Take double negatives as an example: "I don't want to pay no taxes."  Today we would say this is grammatically incorrect. Yet in English's distant past it was acceptable. Yet even today, despite the a fact that the grammar and the semantics reveal a logical contradiction, people use this type of structure, and no one misunderstands the intent.

Does any one misunderstand this grammatical error? From smartphowned.com.

Why then do we penalize ELLs for the same errors?

I've seen speaking assessment rubrics that have grammar components such as "near native-like use of grammar" paired in the same grade band with "virtually error-free usage". So which is it? Are ELLs to be assessed based on native-like speech, which is commonly filled with grammatical inconsistencies? Or should ELLs be assessed based on grammatical precision, a standard to which we rarely hold native speakers?

What are your thoughts about grammar and assessment for ELLs?