Often, this student will turn in late, incomplete, and/or poorly done work, but in response to a different sort of assignment suddenly excel. The cause of this might be that you have suddenly tapped into the strengths of this student's particular learning style. Take this as a sign, and perhaps give this student the opportunity to "explore" this strength more. For instance, if you give them a very different sort of assignment and they excel suddenly, you may have just tapped into one of their "strength" areas. However, and this is perhaps the most frustrating problem in trying to assess a student's needs, LDs tend to manifest themselves inconsistently. In any case, if you suspect that a student might have an LD, and you can find an opportunity to look at both the student's Process and Purpose, teaching strategies will be easier to apply. For instance, looking at how a student reads:
Process: taking a look at the way a student goes through the process of reading. You can have the student read aloud (but be sure that you emphasize that you will not be evaluating or judging her), or have her read quietly as you pay attention to how long it takes her to read the text.
Purpose: after the student has read the text, you can ask questions that will assess comprehension, questions that deal both with retention of content, and the student's ability to interpret, analyze, or personalize the content. (see attachments 3-5 for a list of potential questions, and for a list of possible symptoms to watch for).