Its DUAL if as an instructor you DONT sign off the logbook and give instruction during the flight because the pilot is not up to an acceptable level to be signed off.
Lasor states "where the aim has been achieved, the FI then signs off the logbook"
If its NOT achieved ie a pilot has few problems then you mark it as dual and it is P1 for the pilot when as an instructor I sign him off.
Check LASORS and the JAA FCL 1....................