Actually, not that difficult to get A. Easy to perfrom when most ppl are slack, just need to discuss with your boss what you need to do to get the better grade and set the performance expectation.
Most of the time is the attitude that make the differences, quite a number engineers I worked with always complaint of being under graded but as a third person who work with them, I see a factor in their character that hinders them. But most do not act on the advise and thus maintain what they are getting.
Those who heed the advise does see better performance.