Some children have learning difficulties. These aren't acknowledged. A boy I know had a reading age of 7 in year 10 and the school were still saying he was fine.
ASD is known to have difficulty with social interactions as a hallmark. Eye contact is part of that. I taught DD2 eye contact by rote when she was 4. She wasn't acknowledged as having ASD symptoms until 9, and diagnosed at 11. When she was 4, I used to walk her to school and I'd say "We look at the lollipop lady, we smile, then we can look away again."
Autism and ADHD together can be a real issue. DD2 has just started ADHD medication and the difference it is making is amazing. Today, she's been outside in the sunshine, helping me with some DIY (she hates the sun, so usually would be hiding), offering to get me drinks, watering plants without being asked... You really can't imagine how different it is to 3 days ago, when even asking her to do a small task was like asking her to climb a mountain. ADHD isn't 'a little bit mad, me!', 'oh I'm so forgetful!' stuff. It's a chemical imbalance in the brain.
All those children who have ADHD have deficiencies in their dopamine receptors, which means their brains aren't getting enough fuel to help them learn, concentrate, organise themselves, etc. That means they aren't learning as well as their peers, so they fall behind.