Intelligent Tutoring Systems (ITSs) have seen an increased adoption in various teaching and learning settings, yet research on their user interface design remains limited, particularly in addressing multi-dimensional design aspects and their impact on student motivation. We developed a multi-dimensional guideline for designing optimal interface for supporting learning with intelligent tutors, covering the following four aspects: visibility, learnability, efficiency, and visual presentation. The guideline, developed based on existing frameworks and guidelines, is designed to address students’ cognitive learning needs and preferences. We used the guideline to re-design the user interface of an ITS for elementary mathematics and conducted a mixed-method, within-subject study with 4th-8th graders, comparing the original and re-designed tutor versions. Results demonstrated significant improvements in student motivation in favor of the re-designed version. This work offers a comprehensive design guideline that ITS designers could use to create learning experiences that are both pedagogically effective and motivationally engaging.