Holmqvist, M., & Mattisson, J. (2008). VARIATION THEORY: A TOOL TO ANALYSE AND DEVELOP LEARNING AT SCHOOL. Problems of Education in the 21st Century , Problems of Education in the 21st Century , 7. presented at the June/2008. Retrieved from http://oaji.net/articles/2014/457-1392234817.pdf

Mumba, F., Mbewe, S., Sasser, S., Chabalengula, V. M., & Wilson-Miles, E. (2009). RESIDENT SCIENTISTS’ CURRICULUM AND INSTRUCTIONAL DECISIONS FOR HIGH SCHOOL CLASSROOMS. Problems of Education in the 21st Century, Problems of Education in the 21st Century, 17. presented at the November/2009. Retrieved from http://oaji.net/articles/2014/457-1399915014.pdf