It's not that behaviour alone instigates assessment.
It's that the EP can only see 1 or 2 kids this year. And they have to choose out of 200 - 300 kids.
Someone who only struggles with sitting still and writing, is just not going to be the kid the school are most worried about.
Having said that DS has seen the EP 3 times. (And he only threw 1 chair :) ) And none of the reports were useful at all. They recommended a bunch of generic strategies none of which were tailored to DS.
DD has seen the EP once. A specialist SpLD EP which I waited 2 years for. The recommendations were school should continue to do everything they are doing.
Basically, EPs are just shit. What on earth does the term Educational Psychologist even mean or imply?
The other problem is once you have an EP report and school have followed it's recommendations and they still haven't worked you're really stuck. Because school can now say 'they've done everything they were advised to'.
Without an EP report you can pressure them more to make adjustments :)
But OT reports can be really useful. If he's not writing because it hurts him, then an OT can actually help with that.
An OT can certainly help with the wriggling.
If he's not writing because he doesn't know how to order his thoughts - a teacher really should be able to help him with that. They really shouldn't need EP advice for that.