The FAA produced a document, an "executive summary" of AC 61-65H, dated 8/27/18-- which in its 58 pages does not state that a Student Pilot seeking a Sport Pilot Certificate, or a Sport Pilot seeking an Instructors certificate require a tailwheel endorsement-- of step by step procedures and endorsements required to obtain a sport pilot certificate, and to add additional privileges to a Sport Pilot's certificate.
https://www.faa.gov/sites/faa.gov/files/student_pilot_guidance.pdf
It is also the first link listed here under resources for Sport Pilots and Sport Pilot Instructors
https://www.faa.gov/licenses_certificates/airmen_certification/sport_pilot
Contained within "§ 61.87 Solo requirements for student pilots," is the requirement that a student pilot, prior to solo, must receive instruction, and demonstrate proficiency in "(d)(2) Taxiing or surface operations, including runups;" and "(d)(3) Takeoffs and landings, including normal and crosswind;"
https://www.ecfr.gov/current/title-14/chapter-I/subchapter-D/part-61/subpart-C/section-61.87
There is no requirement for a Student Pilot seeking a Sport Pilot Certificate to obtain a separate Tailwheel endorsement. Obviously, if one trains in a Piper J-3, which is a tailwheel (or tailskid) equipped aircraft, and one is endorsed, "....I have determined she has demonstrated the proficiency of § 61.87(d) and is proficient to make solo flights in a Piper J-3C Cub..." Then one is endorsed as being proficient to operate a small Continental engine, an airplane flown from the back seat, an airplane with a USA-35 airfoil, and most importantly an aircraft with a tailwheel.
Quoting AC 61-65H, For a person with a certificate other than a Sport Pilot Certificate "to act as pilot in command in a tailwheel airplane: § 61.31(i).
This endorsement may be given in a sport pilot aircraft by a sport pilot instructor, or in an airplane by a flight instructor with a rating other than a sport pilot rating. 'I certify that [First name, MI, Last name], [grade of pilot certificate], [certificate number], has received the required training of § 61.31(i) in a [make and model] of tailwheel airplane. I have determined that [he or she] is proficient in the operation of a tailwheel airplane...'"
https://www.faa.gov/documentlibrary/media/advisory_circular/ac_61-65h.pdf