"Milieu teaching" is a practice that involves manipulating or arranging stimuli in a preschool child's natural environment to create a setting that encourages them to engage in a targeted behavior. For example, a teacher might place a desirable toy in a setting to encourage a student to request that toy (where requesting a toy is the desired target behavior). One hundred sixty-one studies reviewed by the What Works Clearinghouse (WWC) investigated the effects of "milieu teaching" on preschool children with disabilities. One study (Yoder, Kaiser, & Alpert, 1991), is a randomized controlled trial that meets WWC evidence standards. That one study is summarized in this report. No studies meet WWC evidence standards with reservations. The remaining 160 studies do not meet either WWC eligibility screens or evidence standards. Fourteen additional studies were reviewed against the pilot Single-Case Design standards. Two studies meet the pilot Single-Case Design standards, two studies meet the pilot Single-Case Design standards with reservations, and 10 did not meet pilot Single-Case Design standards. Studies reviewed against pilot Single-Case Design standards are listed in Appendix D and do not contribute to the intervention's rating of effectiveness. Appended are: (1) Summary of findings; (2) Outcome measures for each domain; (3) Findings included in the rating for the communication/language competencies domain; and (4) Single-case design studies reviewed for this intervention. A glossary of terms is included. (Contains 3 tables, 5 endnotes and 1 additional source.)