Hmm, doesn't sound too bad. I don't have VB installed anymore, and it's been forever since I've done anything like that, but try something like this:
(Please note: I forgot how to reference variables inside an object >_>; such as textbox numbers D: As such, anything with a $ preceding it, will be a var :P)
Code
--VARS--
dim grades[10] as int '10 Grades
dim average as int 'store average of 10 grades
dim loop as int 'loop counter
---
CMD_GRADEINPUT
loop=1 'start loop for adding grades
while loop =< 10 'repeat for 10 grades - 1,2,3,4,5,6,7,8,9,10
grades[$loop] = int(textbox_$loop.text)
loop++
end while
loop=1 'reset loop to #1
label1.caption="Grade #" & loop & " = " & grades[$loop]
CMD_AVERAGEGRADE
average=0 'blank average
loop=1 'reset loop to #1, just in case
while loop =< 10 'initiate loop
average= average+grades[$loop]
loop++
end while
average=(average/10)
loop=1
label2.caption="Average Grade: " & average
Like I said, it's been years since I've done any VB and this is probably wrong, but it should at least give you an idea of how to do it :P
EDIT: Oops, forgot to spit out the details and actually run the average D: