*I've dont this* Even without writing in chalk, water painting on the chalkboard is amazing (read: clean) painting the kids love! Write letters in chalk and have child trace over with water. Just like wet/dry/try from HWOT! So easy
Alphabet Play Dough Mats and many more letter ideas. Have kiddos start out by finger tracing a letter, then using a dry-erase marker and then building the letter using small objects. Practice makes perfect!
Shaving cream writing - learning through sensory play