Christ I was horrendous at 11/12 
I lost money, my pe kit, my lunch, my books etc etc. Worst example I can think of..
I lost my lunch money so I had to use my bus money to eat and didn't think about how I was going to get home, told a teacher I was worried about getting home and got given the £1 I needed. Got on the bus and realised I'd left my pe kit or my school bag on the floor by my locker and just walked off and left it, so I jumped off the bus to get it, got it and the bus was gone...
It was parents evening so I thought I'd just piss about in corridors of school until my parents arrived and catch a lift home with them, I eventually saw them speaking to my science teacher and thought thank god I can go home.
Then I got back from my walk of the corridor again and they'd gone! I'd left my phone at home, so I couldn't ring them and I was stuck now at school 
Eventually my parents got home and realised I wasn't there and realised I must have been classic newyoiker and was still at school, they found me walking home (15 miles) i wasn't too far from school and obviously had no coat
Now I will caveat this with I do have dyspraxia so disorganised is my middle name, but still that kind of takes the piss!
I always wish I could have shown my dad I managed to find coping strategies and im a nurse now but he never got to see that bit of me, he died less than 3 months later from
That parents evening fiasco.
But I did pull it together, I think for me the difference was moving across the country to where my mums family were, I suddenly went from a school that was huge and I was a small fish in a giant
Pond and very strict about everything, to a small school where I was a big fish In a little pond and I flourished. If I'd stayed at the huge school I would not have passed any of my exams I can guarantee that.