The role of parental support in the process of determining the post-school development trajectory of high school students with intellectual disabilities has not yet been sufficiently evaluated empirically. Therefore, the relevance of this study is determined by the growing demand for evidence-based career guidance solutions in inclusive education and for an effective “school–family” partnership model. Purpose of the study: to assess the influence of parental support (informational, emotional, instrumental, and protective/advocacy components) on students’ level of career clarity, as well as to determine how this relationship is moderated by the frequency of school-based career guidance activities. Methodology: The study was conducted using a cross-sectional correlational design. The sample size was N = 156 (9th–10th grade students and their parents). Data were collected through two parallel questionnaires (student/parent); measurement scales were in a 5-point Likert format. Internal consistency reliability ranged from α = 0.71 to 0.89. Statistical analysis included descriptive indicators, Pearson correlations, group differences, multiple regression, and interaction models (variables were z-standardized, robust standard errors applied). Results: The average level of career clarity was M = 3.42 ± 0.66; the composite index of parental support was M = 3.61 ± 0.58. Informational and emotional support showed statistically significant correlations with career clarity (r = 0.34–0.36, p < 0.001). In the regression model, these subscales were identified as key determinants of career clarity (β = 0.20–0.22, p < 0.01). The frequency of school career guidance activities also had an independent positive effect (β = 0.17, p = 0.019), while the “Participation × Support” interaction demonstrated an additional increase (β = 0.14, p = 0.021). The total explained variance of the model was R² = 0.33–0.37. Conclusion: The findings confirm the important role of parental support—particularly its informational and emotional components—in shaping students’ career clarity. Systematizing school-based career guidance activities and implementing transition planning within a “school–family” partnership framework can enhance students’ self-confidence and the quality of their career orientation