14 CFR § 61.423

As a flight instructor with a sport pilot rating you must:

Sign the logbook of each person to whom you have given flight training or ground training.

Keep a record of the name, date, and type of endorsement for:

Each person whose logbook you have endorsed for solo flight privileges.

Each person for whom you have provided an endorsement for a knowledge test, practical test, or proficiency check, and the record must indicate the kind of test or check, and the results.

Each person whose logbook you have endorsed as proficient to operate—

An additional category or class of aircraft;

In Class B, C, and D airspace; at an airport located in Class B, C, or D airspace; and to, from, through, or at an airport having an operational control tower;

An aircraft that is an airplane with a VH less than or equal to 87 knots CAS; and

An aircraft with a VH greater than 87 knots CAS.

Each person whose logbook you have endorsed as proficient to provide flight training in an additional category or class of aircraft.

Within 10 days after providing an endorsement for a person to operate or provide training in an additional category and class of aircraft you must—

Complete, sign, and submit to the FAA the application presented to you to obtain those privileges; and

Retain a copy of the form.

You must keep the records listed in this section for 3 years. You may keep these records in a logbook or a separate document.