if BeginningDate and EndingDate the name of text boxes or dropdown fields then by my understanding it would be:

[vba]="Between " & Format([Forms]![ReportSelection]![BeginningDate],"m/d/yyyy") & " and " _
& Format([Forms]![ReportSelection]![endingdate],"m/d/yyyy")[/vba]

otherwise, if it is a public varible that you pass over, it could be

[vba]
="Between " & Format(BeginningDate(),"m/d/yyyy") & " and " & Format(endingdate(),"m/d/yyyy")
[/vba]