In the decade since alternate assessments based on alternate achievement standards (AA-AAS) were first required, special education teachers have had to develop content knowledge and pedagogical skills to teach academics to students with significant cognitive disabilities. The purpose of this study is to examine the impact that teachers' instructional decisions and beliefs about AA-AAS have on the academic achievement of students with significant cognitive disabilities. A survey of nearly 400 teachers across three states provided evidence of teachers' beliefs, as well as their instructional planning processes for students. Students' learning characteristics were also identified. Survey responses were analyzed in conjunction with students' 2010-2011 scores on their statewide AA-AAS. The results indicated that students with presymbolic communication systems had a lower likelihood of achieving proficiency in English language arts/reading and math than students with abstract symbolic communication. Students with concrete symbolic communication systems had lesser odds of proficiency in ELA/reading but not in math. Teachers who agreed that AA-AAS had an impact on instruction tended to have students with higher achievement proficiency. However, more negative views of the validity of AA-AAS scores were associated with greater odds of proficiency.