=IIf([AttendanceDate]=Weekday([AttendanceDate],[firstdayofweek]),"8.0","0")

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Reply from Alex Hedley:
WEEKDAY takes two arguments, the date in your case [AttendanceDate], the [firstdayofweek] is optional, you don't need this.

Currently if your attendance date is today (11/2/2014) you would have
IIf([AttendanceDate]=Weekday([AttendanceDate]),"8.0","0")

IIf(#11/2/2014#=Weekday(#11/2/2014#),"8.0","0")
IIf(#11/2/2014#=1,"8.0","0")

I don't think this is what you need.

Lets build it up, First calculate if it is a weekday, you can use the BETWEEN keyword.
IsWeekday: Weekday([AttendanceDate]) Between 2 And 6
Then we can use IIF to return 8 else 0 if True.
AttendanceAddition: IIf(Weekday([AttendanceDate]) Between 2 And 6, 8, 0)

Now you can use this value how you wish.