You are only legally required to have single engine climb performance when operating commercially and in a situation where you can not see and avoid obstacles.
Since you are probably providing training for the CPL then the requirments of JAR-Ops for perfromance class B are appropriate for understanding the situation.
In terms of "is this aircraft performing correctly" then the reference is the flight manual which will schedule the gross performance that the aircraft should manage.
Apply your factors to get net performace and confirm that the aircraft is meeting those requirements with ease.
I would not use the certification standards to confirm performace of an established aircraft as the aircraft may have be designed to exceed those minimum performance standards and while grossly underperforming may still meet the minimum requirement.
The flight manual is your legal guide. The Manufacturer will also help.
The friendly pilots at the CAA flight test department will also help you with a better and more specific answer.
Regards,
DFC