There are many types of instructor rating and this is quite a complex area. We have detailed a few of the most useful ones. Get in touch for more info.
Class Rating Instructor (CRI) - Real benefit is it can be added to a PPL. Useful for a club check pilot or for someone that wants to put something back into aviation. You can't instruct new PPL students with a CRI. You can fly the 2 yearly instructional flight that PPL holders require and useful for checking out pilots to a new type within the class. You can conduct differences training with a CRI.
Flying Instructor (FI) - Initially restricted but allows you to instruct as above but you can now teach new PPL students. The restriction is you can't send someone solo. This restriction is lifted with hours and experience. You can also have the restrictions removed for other ratings such as aerobatics and night.
Select the instructor rating you want more info on: