Thank you for your responses! I agree that older students would have more exposure. I am also concerned that older students are simply more physiologically developed than younger students. My concern is that failure to factor in month level age differences would be a major flaw in any achievement test. Surely the research shows statistically significant advantages/disadvantages for older/younger children, even if the difference is 4 or 5 months.
If my children were to be IQ tested for admission to our district's gifted program, they both might have qualifying scores, but only my eldest would gain admittance because his achievement scores are also at the qualifying levels. Frustrating.
I am not familiar with the tests that do factor in age. I have never seen an instance of such tests given my limited experience. I cannot image that it be difficult to do this though! It even seems intuitive that this should be the norm! The Iowa test presents percentiles that compare the student to the entire grade. Test publishers could simply divide students into age groups...say quartiles... and then the test report could say something like: Your child is at the 99th percentile for all first graders...your child falls into the oldest quartile for first graders and scores 90th percentile for this quartile.
