[Grammar] What's the difference between no less ... than and not less than?

[aquariuscmm]

Here is an english grammar question:
John is no less hardworking than his sister, but he failed the exam last month.
in the sentence above, NO less hardworking than means as hardworking as , can I replace it with NOT less hardworking than? i cannot see the difference.

 

[Roman55]

I am not a teacher.

The difference is slight, not to say almost non-existent.

I see a nuance and would use them as follows:

"John is no less hardworking than his sister." They are equally hardworking.

"John is not less hardworking than his sister." He is perhaps more hardworking.