He's year 4 and been told he's working at 4c for maths and literacy after their recent test week. He's never been marked out as particularly bright and apparently "Miss" thought she must have marked it wrong it was so good 
He's not daft, but that's not far behind where DS1 is in year 6 (expected to achieve 4a/borderline 5 ) and I've always thought DS1 was the brighter of the two
He was certainly much earlier with his reading.
So, how reliable is this mid KS marking? Are we setting ourselves up for a fall next year when he appears to go backwards?