Complexity Approach - Regular Past Tense
Complexity Approach for Regular Past Tense Verbs: Van Horne, Amanda Jean Owen et al. “Do the Hard Things First: A Randomized Controlled Trial Testing the Effects of Exemplar Selection on Generalization Following Therapy for Grammatical Morphology.” Journal of speech, language, and hearing research: JSLHR vol. 60, 9 (2017): 2569-2588. doi: 10.1044/2017_JSLHR-L-17-0001
Contrast Cues - Contrast Approach
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Minimal Pairs:
If the child is stimulable for the target sounds (e.g., ‘k’, ‘g’, and ‘sh’), you might consider using the meaningful minimal pairs approach. If the child is NOT stimulable for the sounds, you might use the perception-production minimal pairs approach so that the child can experience success first (Tyler et al., 1987).
Research has shown that three to five word pairs can facilitate generalization in children (Elbert, Powell & Swartzlander, 1991). The authors also reported that some children might require more minimal pairs words.
The SLP should aim for 100 practice trials of the target sounds per session (Sugden et al., 2018). 
While minimal pairs therapy at word level only can be enough to facilitate generalization to untreated words in conversation (Elbert et al. 1990), you might decide to include practice at the phrase and/or sentence level if generalization is slow.  
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Elbert, M., Powell, T. W., & Swartzlander, P. (1991). Toward a technology of generalization: How many exemplars are sufficient? Journal of Speech and Hearing Research, 34, 81-87.
Gierut, J.A.(1989). Maximal opposition approach to phonological treatment. Journal of Speech and Hearing Disorders, 54, 9-19.
Sugden, E., Baker, E., Munro, N., Williams, A.L. and Trivette, C.M. (2018). Service delivery and intervention intensity for phonology‐based speech sound disorders. International Journal of Language & Communication Disorders, 53: 718-734. doi:10.1111/1460-6984.12399
Tyler, A.A., Edwards, M.L., & Saxman, J.H. (1987). Clinical application of two phonologically based treatment procedures. Journal of Speech and Hearing Disorders, 52, 393-409.