Well I was in lowest set for maths GCSE, told I wouldn't stand a chance doing A-Level. Ended up getting a B, and doing fine at A-Level too.
During A-Levels I was told I would struggle with the degree I wanted to do (Aeronautical Engineering), and was predicted a C/D in Business Studies.
Ended up with ABC (the A was in Business Studies) at A-Levels and a 2:1 in Aeronautical Engineering
Take predictions with a pinch of salt.