This paper derives from a large research project focusing on mathematics and science assessment of student learning in three high-need, rural, and urban secondary schools in Manitoba, Canada. The study employed qualitative methods of semi-structured interviews and classroom video recordings of teaching practice experiences of 12 mathematics and science teachers, with the purpose that explore how authentic assessment forms assist effective teaching to monitor and motivate student learning achievement and growth. The results indicate that about 67% (eight out of the twelve of the participants) of the research participants practice the traditional mode of standard assessment that consists of multiple forms of questioning. The participants' rationale relates to speedy evaluations of student work, preparing feedback reports to parents and students, and objectivity of the assessment process. The other 33% (four out of twelve of the participants) of participants practice authentic assessment that concentrates on: (1) Allowing students to apply what they have learned rather than testing their ability to memorize and regurgitate concepts, (2) Allowing students to personalize their knowledge and values, (3) Encouraging group project-based learning and with the use of rubric for evaluating and monitoring, (4) Promoting deep learning to become life-long learners, (5) Recognizing, acknowledging, and validating diversity in student learning styles, interests, and aspirations, and further, authentic assessment is an excellent opportunity to apply communicative technologies such as podcasts and webinars in learning and undertaking investigations in mathematics and science learning. Furthermore, some participants asserted that authentic assessments are time-consuming, labor-intensive, and resource-demanding, aside from the limited resources and lack of training, which are some of the challenges of implementing authentic assessment. Other participants stated that all teachers must be familiar with using all assessment tools. The paper concludes that the principal plays a critical instructional leadership role in a school-wide implementation of authentic assessment.