Well, as far back as I can remember (and I did my student flying in the early 1970s),
FAR 61.87 has said:
Sec. 61.87 - Solo requirements for student pilots.
(a)
General. A student pilot may not operate an aircraft in solo flight unless that student has met the requirements of this section....
(c)
Pre-solo flight training. Prior to conducting a solo flight, a student pilot must have:
(1) Received and logged flight training for the maneuvers and procedures of this section that are appropriate to the make and model of aircraft to be flown; and
(2) Demonstrated satisfactory proficiency and safety, as judged by an authorized instructor, on the maneuvers and procedures required by this section in the make and model of aircraft or similar make and model of aircraft to be flown.
(d)
Maneuvers and procedures for pre-solo flight training in a single-engine airplane. A student pilot who is receiving training for a single-engine airplane rating must receive and log flight training for the following maneuvers and procedures:
(1) Proper flight preparation procedures, including preflight planning and preparation, powerplant operation, and aircraft systems;
(2) Taxiing or surface operations, including runups;
(3) Takeoffs and landings, including normal and crosswind;
(4) Straight and level flight, and turns in both directions;
(5) Climbs and climbing turns;
(6) Airport traffic patterns, including entry and departure procedures;
(7) Collision avoidance, windshear avoidance, and wake turbulence avoidance;
(8) Descents, with and without turns, using high and low drag configurations;
(9) Flight at various airspeeds from cruise to slow flight;
(10) Stall entries from various flight attitudes and power combinations with recovery initiated at the first indication of a stall, and recovery from a full stall;
(11) Emergency procedures and equipment malfunctions;
(12) Ground reference maneuvers;
(13) Approaches to a landing area with simulated engine malfunctions;
(14)
Slips to a landing; and
(15) Go-arounds.
And, as I noted in
another post, slips are included among the Tasks in the
Private Pilot PTS (Task K in Section IV) (that doesn't mean the examiner will
require you demonstrate them, only that slips are among the items your instructor should have trained you to accomplish to the PTS standard and that they're fair game on the flight test).