University physical education classes routinely place students with no racket experience alongside students with years of club play, on the same court, under the same coach, in the same hour. Most lesson plans offer no explicit guidance on when a drill should be made easier or harder, so teachers improvise. This paper converts that improvisation into a repeatable instructional routine. Ideas from representative learning design, functional task difficulty and research on practice variability are combined into four teacher decisions: identifying the constraint that is actually limiting performance, adjusting the smallest constraint that helps, probing whether the improvement survives variation, and re-testing it once support is withdrawn. The paper offers a decision tool—observations, adjustments, stop-and-revise rules and outcome measures—designed for a mixed-ability class. It reports a worked forehand-depth example, a twelve-week progression, a ninety-minute lesson plan and a one-page recording sheet, and it distinguishes winning a rally in practice from genuine learning, stating explicitly when direct technical instruction is the better option. No participants were recruited and no effectiveness data are reported. The paper closes with falsifiable predictions and an evaluation design that accounts for crowded courts and fairness across ability levels.