They don't hold hands when they go through the school hallways; Al's hands are occupied with the task of pushing his wheels as May walks beside him, laughing at some witty remark he made, or some cute, nerdy movie reference.
Or sometimes, it's because May pushes Al, despite his protests ("My arms aren't even tired!"), though she simply laughs and bends down and kisses the corner of his pouting mouth.
Holding hands is so overrated.