National Curriculum levels can be REALLY confusing, especially if you grew up using A-F grades.
There really is very little help online for Parents and Teachers (as we're sure you have found if you've ended up here).
National Curriculum Levels range from level 1 to level 8, with level 8 the most advanced. Each level is split into sub-levels that are like the old grade system with 'a' as the best, 'b' in the middle and 'c' toward the bottom of that level. So a 5a is better than a 5c, and a 5c is better than a 4a.
The other thing to note is that the levels are the same throughout infant, primary, junior and secondary school (and are used right up to year 9 before switching to GCSEs) - this means that someone on a 3a in year 9 should theoretically have the same ability as someone on a 3a in year 2!
To figure that out, you need to know what the national average level is for your child's year / term (this is the same across subjects). For that, we've decided to publish a copy of our progression table (which is part of the PupilAsset system) for everyone to see what is going on. The green blocks show the national "average".