DAX Help for measure

Anonymous - I did it this way, (PBIX attached after sig)

Created this column:

Absent = 
    VAR __Last = MAXX(FILTER('AttendanceMaster',[ChildID] = EARLIER([ChildID]) && [AttendanceDate] < EARLIER([AttendanceDate])),[AttendanceDate])
    VAR __Min = MINX(FILTER('AttendanceMaster',[ChildID] = EARLIER([ChildID])),[AttendanceDate])
RETURN
    IF([AttendanceDate] = __Min,0,([AttendanceDate] - __Last) * 1.)

And then this measure:

Measure = 
    COUNTROWS(
        SUMMARIZE(
            FILTER('AttendanceMaster',[Absent] >= 3),
            [ChildID]
        )
    )

I'm sure there is a more efficient/elegant way to do this, but I ran out of time on my lunch break.  This expression gets the right result of 1 for the sample dataset provided.

Kids with 3+ Consecutive Days Absent =
VAR summarytable =
ADDCOLUMNS (
SUMMARIZE ( Attendance, Attendance[ChildID], Attendance[AttendanceDate] ),
"inarow", CALCULATE (
VAR thisdate =
SELECTEDVALUE ( Attendance[AttendanceDate] )
VAR falselast3days =
CALCULATE (
COUNT ( Attendance[ChildID] ),
ALLEXCEPT ( Attendance, Attendance[ChildID] ),
Attendance[AttendanceDate] <= thisdate,
Attendance[AttendanceDate] >= thisdate - 2,
Attendance[IsPresent?] = FALSE ()
)
RETURN
falselast3days
)
)
RETURN
CALCULATE (
DISTINCTCOUNT ( Attendance[ChildID] ),
FILTER ( summarytable, [inarow] = 3 )
)

Your dates were all consecutive, so this works.  I suspect you are going to need to exclude non-school days, but you can adapt this approach.

If this works for you, please mark it as solution.  Kudos are appreciated too.  Please let me know if not.

Regards,

Pat