My DS is also year 3 and the OT has gone awol so here's what we've been doing. Hope my rambling helps.
Theoderscu "Write from the start" is summat we started at Easter with my DS - also Year 3. I expect it to take a full calender year to complete working on 10 mins a day and repeating some lessons up to 6 times till DS gets his head round the sections he finds really tough. (This means we sometimes spend a full week on just 2 pages!)
Ds also has an a large whiteboard that he does some homework on. I photograph it and email it to teach rather than him writing it down with paper and pencil and getting upset. (My thought is it's the mathmetical process he's learning - not pencil control for that specific lesson iyswim).
At school he uses an alphasmart/laptop for science lessons cos he's GOOD at that crap and taking away the focus from crying over handwriting means he can FLY and it boosts his confidence to be good at something.
His TA does stand over him to make sure he puts in a good 30 mins sustained effort everyday to write in literacy. The focus is either on forming letters correctly OR on self-expression, grammer etc - NEVER both together at this stage.
It's working - his handwriting is still abysmal but he has gone from barely able to write his name to asking to try writing about a topic in class. His writing is deffo improving and my only worry now is what comes after the "write from the start" programme as we'll need something else from the summer term. Our OT has gone AWOL.
We also do lots of simple fine motor skill crafts like sewing and model making weekends and holidays - good for a play date and help his general fine motor skills. Threading beads is a good activity. He thought making Xmas decs at home was fun - his teacher was really pleased with the improvement to his writing skills over Xmas. win- win!!!!
I have to be honest - the sewing is a flippin chore for me as DS gets very frustrated, but it is making a measurabe tangible difference as measured by his teacher so is worth perservering with (even if I do need a glass of wine once he is in bed!).
Tools I'm using (not too dear!)
Formal writing programme you can do at home (to ensure it's done properly if you are anything like me lol!)
www.amazon.co.uk/Write-start-Programme-Perceptual-Handwriting/dp/1855032457
Whiteboard - at least this size (you can get a posher one if you have the funds)
www.amazon.co.uk/Q-Connect-KF03571-Whiteboard-Wooden-600x900mm/dp/B001O3I8KG/ref=sr_1_5?ie=UTF8&qid=1326886037&sr=8-5
Source of simple sewing/beading/craft materials. (pm me if you want some more ideas). Be aware boys go off this sort of craft as they age - do it now before peer pressure reduces his motivation!
LOTS of simple sew your own kits - best site
www.yellowmoon.org.uk/find.asp?src=ADWORDS&name=sew&cid=HYNMPF5Y1CHE2U27L44Y7BDR64FQEM4Y
A couple of useful bits from another good site.
Sew your own teddy
www.craftycrocodiles.co.uk/new-products-c52/felt-teddy-kit-p2184
Bead craft materials
www.craftycrocodiles.co.uk/beadcraft-c38
Plastic saftey needles
www.craftycrocodiles.co.uk/search/needle
When he was younger I used to buy pavement chalk for him to write giant letters/buy value shaving foam for him to write on the sides of the bath. This worked to get the direction letters were supposed to go in.