But the current situation is more analogous to a D student getting a D on the big test. Their first nuclear tests were so weak that there was debate over what they even were, and they almost certainly did not represent a successful test of the intended bomb yield. This latest test was pretty definitely nuclear, but if it was a fusion weapon as claimed then it was again a major failure.

I'm not sure if any other nuclear weapons state has had such a string of failures. Both the US and USSR had successful full yields for their tests of their first fission and fusion bombs. China's first fusion weapon test yielded over 3 megatons.

North Korea's test yielded probably under 10 kilotons, and they're going around bragging about an H-bomb. I'd say that deserves a D, at best.