Jack wears her educational failure as a badge of pride. You see it wasn't Jack being thick, it was the teachers that didn't know how to educate her.
Always someone else's fault.
Where she believes she has acquired all this knowledge that she thinks she has is a mystery too. Left school at 16, 4.5 GCSE's but is an expert on any subject you like to mention. Seen it, done it, know it, tried it, yet she has hardly moved out of Southend. I don't mean for a holiday, a few weeks shacked up in a shags house, or months in an hotel while going to rehab. I mean travelling, seeing the world, gaining experiences and meeting people.
Even when she was taken to Tanzania, she managed to centre herself by comparing her own experiences with that of a starving mother. Didn't use the experience to educate herself, just to tell people how hard she has had it, dismissing the true poverty that was staring her in the face.