I used to swear by Moleskine A5 notebooks but the quality seemed to change so I switched to Leuchtturm1917 [1] several years ago and haven't looked back
I was an extra in this movie - some of the school scenes (eg. the hallways during the sprinkler scene, which was great fun to film!) plus some interior classrooms too - were filmed on a sound stage at Pinewood Studios in London [1].