Researchers have found that hearing students in pre-kindergarten classes who receive instruction in both English and ASL score significantly higher on the Peabody Picture Vocabulary Test than hearing students in classes with no sign instruction. Specifically, the studies of Dr. Marilyn Daniels demonstrate that adding visual and kinesthetic elements to verbal communication helps enhance a preschool child's vocabulary, spelling and reading skills.

Daniels, M. (1994). The Effects of Sign Language on Hearing Children's Language Development. Communication Education, October, v43 n4, p291 (8).

Daniels, M. (1996). Seeing Language: The Effect Over Time of Sign Language on Vocabulary Development in Early Childhood Education. Child Study Journal, 26, 193-208.

Daniels, M. (2001). Dancing with Words: Signing for Hearing Children's Literacy. Westport, Connecticut: Bergin and Garvey.

Feltzer, Laura, MBR Reading Program: How Signing Helps Hearing Children Learn to Read - Research Summary

Felzer, L. (1998). A Multisensory Reading Program That Really Works. Teaching and Change, 5, 169-183.

 
Hafer, J. (1986). Signing For Reading Success. Washington D.C.: Clerc Books, Gallaudet University Press.

Koehler, L., and Loyd, L. (September 1986). Using Fingerspelling/Manual Signs to Facilitate Reading and Spelling. Biennial Conference of the International Society for Augmentative and Alternative Communication. (4'th Cardiff Wales).

Wilson, R., Teague, J., and Teague, M. (1985). The Use of Signing and Fingerspelling to Improve Spelling Performance with Hearing Children. Reading Psychology, 4, 267-273.