Two focus groups were conducted with special needs teachers to: (a) identify barriers to learning for autistic pupils, (b) consider broad assessment domains and specific skills or behaviours which teachers consider important for these pupils, and (c) give their opinions on teacher assessments. Data analysis resulted in six main themes: (a) barriers to learning, (b) teacher priorities for autistic pupils, (c) ways of overcoming barriers, (d) the concept of 'true mastery', (e) assessing the bigger picture, and (f) practicalities of assessment. Results showed that teachers have priorities for the pupils they know well and concerns about the assessments they regularly use. To ensure face and content validity of teacher assessments, and for assessments to be useful to and valued by the teachers who use them, it is recommended that teachers have opportunities to input during various aspects of the assessment development process.