Once I changed your table definition for the Grade column from VARCHAR to NUMERIC(10,2), this works for me:

WITH cte AS

(

SELECT CourseDate, PersonID, Grade,

ROW_NUMBER() OVER(PARTITION BY CourseDate ORDER BY Grade) AS RowNum,

COUNT(*) OVER(PARTITION BY CourseDate) As cnt

FROM estats

)

SELECT CourseDate, AVG(Grade) AS Median

FROM cte

WHERE RowNum IN((Cnt + 1) / 2, (Cnt + 2) / 2)

GROUP BY CourseDate

ORDER BY CourseDate;

It returns medians of 90, 76, and 90.5 for CourseDates of 2010-03-01, 2011-03-02, and 2012-03-01, respectively.

I'm not sure why you would define the Grade column to be VARCHAR() when all your data are numerics. I haven't looked into this more, but it may be that this is a source of error. I suspect that you're getting an implicit conversion from VARCHAR() to INT, which leads to loss of necessary accuracy when the final AVG() function is called.

Rich