Modality Matters: How Text, Audio, and Video Interactions Shape Student Engagement and Performance with AI Tutors in 6-8 Mathematics. - Tyree S. Cowell; Kole Norberg; Rae Bastoni; Unekwu-Ojo Shaibu; April Murphy; Stephen Fancsali; Steve Ritter 001; Husni Almoubayyed (AIED, 2026)