Learners at Grade 12 level persistently show a weak conceptual understanding of geometric concepts (DNEA, 2011, 2012, 2014). The study was guided by Bruner’s (1960) Constructivist Theory, using Understanding by Design teaching approach to explain Geometrical concepts. The study was qualitative, using non-equivalent pre-test and post-test quasi-experimental design. Cluster random sampling was used to select a sample of 176 Grade 12 learners from two purposively selected secondary schools. The findings revealed that at 95% confidence level.

• Bruner, J. (1960). The process of Education. Cambridge, MA: Harvard University Press. Retrieved from, http://ti.psychology.org/bruner.html
• Clayton, S. (2011). Understanding by Design: Designing Learning, Assessment and Teaching for Understanding. Retrieved from, http://www.ascdsingapore.org/images/Vol16pg63-66.pdf
• Cohen, L., Manion, L., & Morrison, K. (2011). Research Methods in education (7th ed.). Canada: Routledge.
• DNEA. (2011). Examiner’s report: Mathematics NSSC core and extended examinations. Windhoek: DNEA.
• DNEA. (2012). Examiner’s report: Mathematics NSSC core and extended examinations. Windhoek: DNEA.
• DNEA. (2013). National and regional Distribution of Symbols November 2012 NSSC Ordinary level (Gd. 12) Full Time. Retrieved from, http://www.dnea. gov.na/stats/ Reports/201312/Ordinary/distr_4.pdf
• DNEA. (2014). Examiner’s report: Mathematics NSSC core and extended examinations. Windhoek: DNEA.
• DNEA. (2014). National and regional Distribution of Symbols November 2014 NSSC Ordinary level (Gd. 12) Full Time. Retrieved from, http://www.dnea. gov.na/stats/ Reports/201412/Ordinary/distr_4.pdf
• EMIS. (2014). Education statistics. Windhoek: Directorate of Planning and Development: Ministry of Education.
• Gay, L. R., Mills, G. E., & Airasian, P. (2009).  Educational research. Competencies for analysis and applications (9th ed.). New Jersey, USA: Pearson Education Inc.
• Idris, N. (2009). The Impact of Using Geometers’ Sketchpad on Malaysian Learners’ Achievement and Van Hiele Geometric Thinking. Journal of Mathematics Education. 2(2), 94-107.
• Karue, N., & Amukowa, W. (2013). Analysis of Factors that Lead to Poor Performance in Kenya Certificate  of  Secondary Examination in Embu District in Kenya. Retrieved from,   http://www.tijoss.com/TIJOSS%2013th%20Volume/Amukowa.pdf
• Keskin, S. (2006).  Comparison of several Univariate normality tests regarding Type I Error and power of the test in simulation based small samples. Journal of Applied Science research 2(5), 296-300.
• Mateya, M. (2008).  Using the Van Hiele theory to analyse geometrical conceptualisation in Grade 12 learners: A Namibian perspective. Published Master’s thesis, Rhodes University, Johannesburg.
• McTighe, J., & Wiggins, G. (2012). Understanding by Design framework. Retrieved from http://www.ascd.org/ASCD/pdf/siteASCD/publications/UbD_WhitePaper0312.pdf
• Myers, R.Y. (2009). The Effects of the Use of Technology In Mathematics Instruction on Learner Achievement. Published PhD Dissertations. Florida International University. Retrieved from http://digitalcommons.fiu.edu/etd/136.
• National Institute for Educational Development (NIED). (2010). Namibian Secondary School Certificate Mathematics Syllabus Ordinary level. Okahandja: NIED.
• Ngololo, E. N., Howie, S. J., & Plomp, T. (2012). An evaluation of the implementation of the National ICT Policy for Education in Namibian rural science classrooms. African Journal of Research in MST Education,16(1), 4–17.
• Ogdol, E.,R., & Lapinid, M., R. (2013). Developing students’ Mathematical understanding on linear equations in two variables using a UbD unit plan. Paper Presented at Research Congress, March 7-9, 2013. De La Salle University Manila. Retrieved from http://www.dlsu.edu.ph/conferences/dlsu_research_congress/2013/_pdf/LLI/LLI-II-014.pdf
• Pearson, E., Dorrian, J., & Litchfield, C. (2011). Harnessing Visual Media in Environmental Education: Increasing Knowledge of Orangutan Conservation Issues and Facilitating Sustainable Behaviour through Video Presentations. Environmental Education Research, 17(6), 751-767.
• Perry, M. J. M. (2013). Effects of Visual Media on Achievement and Attitude in a Secondary Biology Classroom. Published Master’s thesis. Ohio University.
• Roblyer, M. D., Edwards, J., & Havriluk, M. A. (2010). Integrating educational technology in teaching. Colombus, OH: Merrill.
• Simataa, A., & Simasiku,  L. (2012). An analysis of the management of the Namibian information communication technology school curriculum planning. International Journal of Global education, 1(2), 7-14.
• Social Studies Center for Educator Development (SSCED). (1999). Texas Social Studies Framework, Kindergarten-Grade 12: Research and Resources for Designing a Social Studies Curriculum. Austin, TX: Texas Education Agency.
• United Nations. (2015). Sustainable Development Goal 4: Ensure inclusive and equitable quality education and promote lifelong learning opportunities for all. Retrieved from, https://sustainabledevelopment.un.org/sdg4
• Wenglinsky, H. (1998). Does it compute? The relationship  between educational technology and student achievement in Mathematics. New Jersey: Educational Testing Service.
• Wiggins, G., & McTighe, J. (2003). Understanding by Design framework. Retrieved from, http://www.ascd.org/readingroom/books/wiggins98book.html#chap1
• Wiggins, G., & McTighe, J. (2005). Understanding by design. Alexandria, VA: ASCD.

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