I believe in trying to measure aspects like these in an equation to good results
would be something like, every person starts off with a mark, that they would get if they didn't work at all, lets say 80 for a smart student and 70 for an average, 60 for a stupid student.. then from here depending on the amount of work you do, your results will change, for example
Smart student does a bit of work and 80+4 = 84
Average Student does a lot of work 70+12 = 82
Stupid Student does little work 60+2 = 62
From here, we can say, that work is not defined by it's nature and origin, whether it be forced by obsessive parents or whatever, it's still work... although it may change the quality of the work, assuming the equation to how much work you do is something like time spent + efficiency = work done, and perhaps a student who is forced to do work will do less efficient work than one who is self-motivated but its really unimportant for the end result.
There are also certain traits/circumstances that can help students do well, including good memory, concentration, lucky (;D) organization, tutor ETC
So then we goo
Smart Student has a decent memory, bad organization, is not so lucky no tutor etc, Average has good memory great organization and tutors and the Stupid student just happens to have a decent memory and no tutors and bad organization soo then we gooo
Smart Student is 80+4+5 = 89
Average Student is 70+12+8 = 90
Stupid Student is 60+4+7 = 71
SO THEN I SAYY!!! There are many circumstances in which results can come from, but a smart stupid has the advantage over the average student, and the average student would have to do more work than him to beat him...there are also limitations created, that for example, A stupid stupid would have to do so much work and be soo lucky that its unrealistic, and high results are achievable but not very high, and smart students unless something goes wrong will get a decent result without much effort and then a lot of potential to get a good mark... thats what I think ;p
I also think that ur statement is created by someone who is attempting to excuse himself from his bad results ;/