given that the standard error is calculated as sd/sqrt(n), the standard error in different sub groups will differ according to their sd and how big n is for the sub-group. (I think)

the question is

"By how many standard errors is the mean experience of teachers in "regular classess with teacher's aides" different from the mean experience of "teachers in small classes"

For the question above, which standard error would you use? The standard error of "regular classess with teacher's aides" or "teachers in small classes"?