sensory issues

I'm in the U.S. and we have laws here that are likely to be different from where you live. I've had ups and downs with my school district over the years for both of my boys, who are now much better & I've learned lots, but not sure how this translates to another country...Here's my attempt to be helpful:

You wrote this as Sensory Issues & yes, he seems like a classic sensory "seeker" which is manifesting in some behaviour issues at school and some benign things like sour foods. At age 9, children should be able to attend long enough to learn and your son sounds bright so there's a breakdown somewhere and only a doctor can really pinpoint this for you. Can you see a Developmental Paediatrician?  That's probably going to be the best route, although a Paediatric Neurologist would probably help, too. 

I say that my second son is like an onion, he has layers (like Shrek) - the more doctors we took him to, the more diagnoses we found...which is bad but it's also good!! His medical journey has helped his behavior greatly, though he's not perfect. In his case, it was a combination of visual issues, Coeliac Disease and very mild Cerebral Palsy, not even found until he was six. He has neurological, fine motor and muscle tone issues plus ADHD, eczema, nut allergies and I even wonder if there's more... The one thing for which he was tested and not found to have is auditory processing problems. No official diagnosis, but I feel comfortable saying he has dysgraphia, which your son may have, too.

The reason I give his history is to see if any of that resonates with you, as my son is 8 and sounds a little like your son. When he started public Kindergarten, I was insistant that he have accommodations for the issues we knew about and it took time but his teacher was a huge support and he got them. As the other diagnoses rolled in, we added them to his 504 Plan. (It's what you can use to receive support in school here if you don't have a diagnosed learning disorder and it's part of the Americans with Disabilities Act, so it's to make a level playing field for children with medical conditions that can affect any part of school)

Now an Occupational Therapist works with him on fine motor skills like writing and tying his shoes, plus his sensory issues (he's more of an avoider than a seeker). His vision issues, which are Amblyopia & Strabismus, got better with corrective surgery and vision therapy (the latter is somewhat unorthodox and insurance pays very little so it was thousands of dollars for us but in the end it helped with his reading). He does not have dyslexia but like your son is a strong reader now, however is spelling is poor and now the school is helping with that. He had behavior plan/modifications in place, but doesn't seem to need them now and the teacher knows all about his "quirks" so she can factor them in when she teaches. He sits near her desk, he's not too close to friends, she cut back his weekly word study writing exercises for a while, but built it back up so it wasn't overwhelming him...etc. And she knows now not to tap his shoulder to redirect him - he apparently JUMPED at the contact (drs. can't even feel his abdomen at check ups , he's soooo sensitive to light touches, cold hands, surprise touch, etc.)!  And, yes, in preschool if the teachers tried to move him to a "time out" it would become physical with him flailing and fighting against being touched, not the actual punishment. 

Don't change your son's diet just yet. You want to see if he has any condition, including food-related (we took wheat out of my son's diet for months, then found it didn't help his eczema so added it back only to find his Coeliac Disease a year later and he would never have known if it weren't for the "regular" diet)  Recording a food diary can show some insight for now, but don't eliminate foods yet. 

Good Luck!!  Please keep us posted - and hang in there! Especially with him home from school this has to be SO HARD on you both!  (Are you getting home instruction from the school in your house? He's probably very capable of learning under the RIGHT conditions)