Autofill records Is this possible???

[Blackwidow]

right this is a little difficult to explain but basically what I have is a form where you select the class and then the module and then the students enrolled in the class are llisted in a subdatasheet with an attainment column next to it... on occasions there maybe 125 Students who have achieved an "A" is there a way to just to select "A" from a drop down box or something (Vague I know bare with me brain wave!) select each attainment grade next to the student who has achieved the "A" grade and then for it to autofill all the highlighted with the grade "A"... or should I just go back to dream land???