The purpose of this study was to investigate the assessment practices of mathematics teachers who also teach AP Statistics. My focus was to explore the teachers conceptions of assessment in mathematics and AP Statistics, the way that the teachers carried out assessment in the two courses, and the factors that influenced the teachers classroom assessment practices in the two kinds of courses. Though there has been a lot of research on assessment practices, there has not been a study that has looked at the assessment practices of teachers in both mathematics and AP Statistics. For example, we do not know whether the way teachers view assessment in mathematics is the same as the way they view assessment in AP Statistics.Two teachers who were teaching mathematics and AP Statistics participated in this study from November 2008 to February 2009. Each teacher was interviewed two times for about 90 minutes each. Interviews focused on the teachers conceptions of mathematics, statistics and assessment. Each teacher was observed 12 times in class. Artifacts were also collected from each teacher. Three frameworks were used to analyze the data a theory of intellectual development, a mathematics taxonomy framework, and the six assessment standards by (NCTM, 1995). Data were analyzed by using an analytic induction method. The results of the study indicated that there was no difference between the teachers conceptions of assessment in mathematics and AP Statistics. The main aim of assessment was to promote students learning. Two forms of classroom assessment were identified formal and informal assessment. Formal assessment involved the use of homework, quizzes, and tests. Informal assessment involved oral questions and listening to students conversations. Assessment questions (oral and written) in AP Statistics and mathematics mostly assessed recall of information, comprehension of information and routine use of procedures. Factors that influenced the teachers assessment practices included time, textbook publishers tests, and teachers pedagogical content knowledge. The findings in the study suggest that there is need to bring awareness to the teachers to think about the types of assessments they use and the type of thinking skills that they assess.