Naomi,

That's going to give the 15th day of the month on average which probably isn't what she's looking for.

>select EmployeeID, avg(CheckInTime) as Avg_CheckInTime from CheckIns where CheckInTime between @StartOfTheMonth and @EndOfTheMonth group by EmployeeID

Victoria - if you are looking for the average time of day they are checking in use a query like

declare @tClock table ( t1 datetime )
insert into @tClock values ( '1/1/2009 08:00:00' )
insert into @tClock values ( '1/2/2009 08:01:00' )
insert into @tClock values ( '1/3/2009 08:02:00' )
insert into @tClock values ( '1/4/2009 08:30:00' )
select avg( datepart( hour, t1 ) * 60 * 60 + datepart( minute, t1 ) * 60 + datepart( second, t1 ) ) / 3600.0
   from @tclock

which is time in decimal hours which you can convert back into a hh:mm:ss format.