Speech and language development is considered a useful indicator of a child's overall development and cognitive ability by experts and is related to school success. Identification of children at risk for developmental delay or related problems may lead to intervention services and family assistance at a young age when chances for improvement are best. This rationale supports preschool screening for speech and language delay, or primary language impairment/disorder, as a part of routine well child care. This evidence synthesis focuses on the strengths and limits of evidence about the effectiveness of screening and interventions for speech and language delay in preschool age children. Its objective is to determine the balance of benefits and adverse effects of routine screening in primary care for the development of guidelines by the U.S. Preventive Services Task Force (USPSTF). The target population includes all children up to age 5 years without previously known conditions associated with speech and language delay, such as hearing and neurological impairments. The evidence synthesis emphasizes the patient's perspective in the choice of tests, interventions, outcome measures, and potential adverse effects, and focuses on those that are available and easily interpreted in the context of primary care. It also considers the generalizability of efficacy studies performed in controlled or academic settings and interprets the use of the tests and interventions in community-based populations seeking primary health care. Key questions addressed include: Key Question 1. Does Screening for Speech and Language Delay Result in Improved Speech and Language as well as Improved Other Non-speech and Language Outcomes? Key Question 2. Do Screening Evaluations in the Primary Care Setting Accurately Identify Children for Diagnostic Evaluation and Interventions? 2a. Does Identification of Risk Factors Improve Screening? Key Questions 2b and 2c. What Are Screening Techniques and How Do They Differ by Age? What Is the Accuracy of Screening Techniques and How Does It Differ by Age? 2d. What Are the Optimal Ages and Frequency for Screening? Key Question 3. What Are the Adverse Effects of Screening? Key Question 4. What Is the Role of Enhanced Surveillance by Primary Care Clinicians? Key Question 5. Do Interventions for Speech and Language Delay Improve Speech and Language Outcomes? Key Question 6. Do Interventions for Speech and Language Delay Improve Other Non-Speech and Language Outcomes? Key Question 7. Does Improvement in Speech and Language Outcomes Lead to Improved Additional Outcomes? Key Question 8. What Are the Adverse Effects of Interventions? Key Question 9. What Are Cost-Effectiveness Issues?