My kids were evaluated very young. easy child 2/difficult child 2 and difficult child 3 were only 4. They did a WPPSI test, which in each case was administered by a trained psychologist. In difficult child 3's case it was part of a multidisciplinary evaluation.
The WPPSI test was designed for pre-schoolers and early school years. It turned out to be invalid in difficult child 3's case because he did not have the expected language skills at that time, to be able to understand the questions.
easy child 2/difficult child 2 also did a Vineland Adaptive Skills test as well as a couple of others. She scored very high and on the basis of those results, was accelerated into school.
The School District may not want to/be equipped to administer a WPPSI. But a multidisciplinary assessment can be done at this age, and much younger. Be prepared to need to have it done over, when he's older, but you need assessment now in order to get on top of whatever is causing these problems. A behaviour assessment may give some useful information and I would accept their offer to do this, but for the really important potentially diagnostic information, I'd push for much more. The SD may not do it, though - you may have to go private.
I'm not familiar with your rules & regs, so get more info from your own schooling area.
Marg
