This study quantified changes in tennis skills and dose of practice in adults with developmental and intellectual disabilities following an 8-week adapted tennis program. Twenty-seven adults with disabilities (mean age 24.7) participated in an 8-week adapted tennis program (1-hour, twice a week). Participants’ racquets were equipped with sensors that measured the number of shots during the program (dose). Pre- and post-test tennis skill assessments (process scores) were conducted for the forehand and backhand. All participants showed significant improvements in forehand and backhand process scores. Level of function, but not age or disability type, was associated with forehand and backhand process scores. The number of forehand shots performed during the adapted tennis program did not change across the program. The number of forehand shots was associated with age and disability type, but not level of function. The number of backhand shots (dose) was not associated with age, disability, or level of function. The number of forehand or backhand shots (dose) was not associated with changes in forehand or backhand process scores, respectively. This study provides evidence of the efficacy of this adapted tennis program to develop fundamental tennis skills in novice players with developmental and intellectual disabilities.