This paper reports on a Mixed Methods study involving an investigation into the attitudes of advanced level biology teachers towards assessment and describes the teachers' experiences while being engaged in Assessment for Learning (AfL) practices such as sharing of learning objectives and peer- and self-assessment. Quantitative data were collected from 40 teachers using the researcher-constructed Teachers' Attitudes towards Assessment Questionnaire. Qualitative data were collected through discussions and interviews from six teachers who implemented AfL strategies. The findings revealed that advanced level biology teachers displayed highly favourable attitudes towards assessment. The teachers engaged in AfL had similar attitudes towards assessment as those who were not. Further there were no statistically significant differences in the teachers' attitudes towards traditional assessment and AfL. The teachers, however, described positive experiences while conducting AfL and highlighted the usefulness of practices such as the sharing of learning objectives and students' engagement in self-assessment. They also expressed the limitations of operating within a high-stakes examination environment. These findings have shown that the use of AfL methods in advanced level biology classrooms has value and can be practiced along with traditional assessment methods.