This study developed scenario-based assessment items to measure students' attitudes toward mathematics and mathematical practices, while evaluating the validity of the assessment. Familiar mathematical learning situations comprised scenarios for first-year high school students. For each scenario, we created multiple-choice items to evaluate eight components: interest, self-efficacy, meta-affect, persistence, challenge, conflict resolution, cooperation motivation, and enjoyment of mathematical culture. Factors of the evaluation elements were matched with the choices of items. The global citizenship factor was evaluated in a single scenario. Moreover, the content validity ratio, content validity, and agreement rate were obtained through two rounds of Delphi surveys on the developed items. After the Delphi survey, a preliminary test was conducted with high school students to confirm that the participants' responses to the items aligned with the researchers' assumptions. Based on these findings, we make recommendations for online implementation of the scenario test developed in this study.