Apel & Henbest evidence teaching affixes in early elementary reading programs.
Lyster et al. evidence positive long-term benefits for morphological awareness training in preschool.
Complex syntax research on preschool and early-elementary children has been gaining tons of momentum lately. Steel et al. show that children with language impairment (ages 5;1–8;10; mean 6;10) have difficulties with complement clauses,and discusses why you should be targeting these in therapy.
Edwards & Rosin evidence African American English (AAE)-speaking preschoolers' gains in phonological awareness and word comprehension measures following a Mainstream American English dialect awareness program (“Talking and Learning for Kindergarten”).
Edwards, J.R. & Rosin, P. (2016). A Prekindergarten Curriculum Supplement for Enhancing Mainstream American English Knowledge in Nonmainstream American English Speakers. Language, Speech, and Hearing Services in Schools, 47, 113–122.