English language education in Thailand is rated poorly internationally and needs improvement. Research identifying the reasons for the l highlights assessment as a key concern since assessment has washback effects on learning. However, little is known about the assessment practices teachers use. This paper has three goals: to identify the assessment practices used, to identify the reasons underlying teachers' decisions about assessment, and to promote assessment practices likely to have positive washback. A survey of 329 teachers found that two-thirds of students' scores came from tests, but that all teachers used some form of continuous assessment. From interviews with 29 teachers, teachers used tests to reduce their workload and to prepare students for the national ONET exams, while using continuous assessment to motivate students and to prepare them for real-world uses of English. Based on evidence that continuous assessment is more likely to promote positive washback, 303 assessment activities designed by teachers were analyzed for potential benefits. Rating the activities on five criteria, 39 assessment activities with potential positive washback were identified, designed into attractive formats, and disseminated to teachers. Using these activities with positive washback is likely to have beneficial effects on English language education in Thailand.