Try

Variable: rnUnSt
Value to Store = IIF(rnLines=1, 1,0)
Initial Value = 0
Calculation Type: Sum
Reset At:Group: Tutor

>I like your ideas. Unfortunately the variable shows the number of sign-ins (count of detail line) and not the number of students. It seems this simple task is a big challenge in the FRX.
>
>Mon
>
>>It can also be done with Report Variables. Try

>>Variable: rnLines
>>Value to Store = 0
>>Initial Value = 0
>>Calculation Type: Count
>>Reset At:Group: Student
>>
>>Variable: rnUnSt
>>Value to Store = IIF(rnLines=1, 1,0)
>>Initial Value = 0
>>Calculation Type: Count
>>Reset At:Group: Tutor
>>