There is no hard and fast cut off, but I am very hesitant to evaluate a child before he or she reaches second grade and maybe seven or seven and a half. Before this age, it’s very difficult to interpret test results for a few reasons. For one thing, the expectations in reading and math are pretty basic, so every test item can have a huge impact on score. For example, if a six-year-old misses two words on a reading test, there are certain times when this will result in a drop in score to the level that looks like a disability. This might be nothing, however, since it could be caused by a common mistake like mixing up “d” and “b” or not understanding silent “e” on the end of a word. These are often just something it take a student a few times to understand, and when he or she does, then a reading score could increase dramatically. I see these big jumps in performance after a “Eureka” moment all the time. I also see a lot of first grade readers who forget a rule occasionally. If this is still happening much later, then it’s a good reason to test.
Expectations are also low enough that sometimes a student can’t get a very low score. Imagine that on a given test, the average six-year-old gets five items correct. Since tests are scored based on the typical performance of a test taker at a given age, this can often mean that getting only one or even no items correct is still not a very low score. If twenty percent of test-takers get no items correct (which is only five items off of the Average) then a raw score of zero, would still keep a child in the twentieth percentile in the Average or Low Average range.
Finally, there’s just a lot of development that happens in the first few years of school and life. I’ve given attention tests to very young children before, and at first was always amazed how poorly they appeared to do. Very young children really do have poor memories, bad attention spans and are not very good at most cognitive tasks. However, when I’ve scored these kids, they are almost always just average. It’s simply typical for children in Kindergarten and first grade to have short attention spans, make lots of mistakes and have trouble figuring things out. These will all improve rapidly, but usually when I’ve had to evaluate children at five or six, the real reason for their difficulty is that they are five or six.
It’s also best to save an evaluation so that it can be given appropriately when the time is right. If a child is tested at six, and then again just a little while later, there can be a learning effect. It might not be dramatic, but just a little familiarity with a certain kind of task or puzzle can impact performance enough to throw off the results. Ironically, testing a child too early can create a situation where when we test him or her at the right time, the actual issue won’t show up. This is all on top of all of the class (often one or two days) that a child is going to miss due to evaluation.