It can be difficult to tease out reading problems at this age - because the students are "just out the gate" so to speak, it is fairly easy to score well on many measures of reading. But, there are red flags that can be considered (many that you you listed such as sight word difficulty, missing/inserting sounds when reading etc) as well as tests that measure the underlying processes for reading.
My sense is that a school evaluation would not yield you the information that you need. Instead, would be better off seeking help from a reading specialist, neuropsychologist or even maybe a Speech and language pathologist with an expertise in literacy/reading. They would most likely test the underlying phonological skills and naming skills needed for reading. THey would also look at patterns within his cognitive profile (for instance relatively weak processing speed compared to verbal comprehension) for clues.
Here is some info on some of the tests:
http://www.concordspedpac.org/Whichtest.htmHope this helps!!
